Bismuth subsalicylate,a low-toxicity catalyst for the ring-opening polymerization (ROP) of l-lactide (l-LA) with aliphatic diol initiators: synthesis,characterization, and mechanism of initiation

The ring-opening polymerization (ROP) of l-lactide (l-LA) was induced by the catalytic action of bismuth subsalicylate (BiSS) using linear aliphatic diols [HO(CH₂)_nOH, where n = 2, 3, 4, 5, 6, and 8] as initiators and chain transfer agents. The theoretical and experimental degree of polymerization (DP) in all samples of α,ω-hydroxy telechelic poly(l-lactide) (HOPLLAOH) had a good agreement in all samples, an effect attributed to the interaction of BiSS with HO(CH₂)_nOH inducing a transfer reaction. HOPLLAOH was synthesized and characterized by a range of analytical techniques, confirming the insertion of methylene groups from the initiator into the main chain of the polyester. The glass-transition temperature (T_g) of HOPLLAOH was found to be proportional to the number of methylene groups present in the diol. Various parameters regarding the ROP of l-LA were studied, such as temperature, time of reaction, amount of catalyst, and the nature of the diols. A kinetic study of the reaction allowed the determination of the rate constants (k) and activation energy (E_a). A mechanism of initiation is proposed based on a computational study using density functional theory (DFT), evidencing the role of the alkyl diol as an initiator, producing an alkoxide (Bi–OROH). This species then acts as a nucleophile, attacking the carbonyl group, inducing its insertion, and ultimately completing the ring-opening of l-LA.

Bismuth subsalicylate (BiSS) acted as a catalyst in the ring-opening polymerization of l-lactide (l-LA) in the presence of alkyl diols as initiators.     

pH-responsive polymeric vesicles from branched copolymers

A new type of branched copolymer, poly(l-lactide)₂-b-poly(l-glutamic acid) (PLLA₂–PLGA), based on polypeptide PLGA is synthesized by the ring-opening polymerization (ROP) of N-carboxyanhydride of γ-benzyl-l-glutamate (BLG–NCA) with amino-terminated PLLA₂–NH₂ and subsequent deprotection. The branched copolymer is characterized by ¹H NMR, FTIR and GPC measurements. The self-assembly of the copolymers in aqueous media has been systematically discussed. A pyrene probe has been used to demonstrate the aggregated formation of PLLA₂–PLGA in solution by measuring the critical micelle concentration (cmc). The morphology and size of the micelles have further been studied by transmission electron microscopy (TEM), dynamic light scattering (DLS) and field emission scanning electron microscopy (ESEM). We demonstrated that the Rh of the vesicle is depending on solution pH and salt concentration. The vesicles show good stability with remained shapes and sizes during the lyophilizing process. These vesicles have great potential in the application of drug delivery.

A new type of branched copolymer, poly(l-lactide)₂-b-poly(l-glutamic acid), based on polypeptide PLGA is synthesized by the ring-opening polymerization of N-carboxyanhydride of γ-benzyl-l-glutamate with amino-terminated PLLA₂–NH₂ and subsequent deprotection.     

High voltage,solvent-free solid polymer electrolyte based on a star-comb PDLLA–PEG copolymer for lithium ion batteries

In this work, a novel star-comb copolymer based on poly(d,l-lactide) (PDLLA) macromonomer and poly(ethylene glycol)methyl ether methacrylate (PEGMA) was prepared, and the electrochemical properties were studied, with the aim of using it as a solid polymer electrolyte in lithium ion batteries. The six-arm vinyl functionalized PDLLA macromonomer was synthesized by a ring-opening polymerization (ROP) of d,l-lactide and subsequently an acylation of the hydroxy end-groups. A series of free-standing solid polymer electrolyte membranes from different ratios of PDLLA, PEGMA and LiTFSI were prepared through solvent-free free radical polymerization under UV radiation. The chemical structure of the obtained polymers was confirmed by ¹H NMR and FTIR. The as-prepared six-arm star-comb solid polymer electrolytes (PDLLA-SPEs) exhibit good thermal stability with T_d^5%s of ∼270 °C and low T_gs of −48 to −34 °C. The electrochemical characterization shows that the PDLLA-SPEs possess a wide electrochemical window up to 5.1 V with an optimal ionic conductivity of 9.7 × 10⁻⁵ S cm⁻¹ at 60 °C at an EO/Li⁺ ratio of 16 : 1. Furthermore, the all-solid-state LiFePO₄/Li cells display extraordinary cycling and rate performances at 60 °C by curing the PDLLA-SPEs directly on the cathode. These superior properties of the six-arm star-comb PDLLA-SPE make it a promising candidate solid electrolyte for lithium batteries.

In this work, a novel star-comb copolymer based on PDLLA macromonomer and PEGMA was prepared, and the electrochemical properties were studied, with the aim of using it as a solid polymer electrolyte in lithium ion batteries.     

Glycol-functionalized ionic liquids for high-temperature enzymatic ring-opening polymerization

Enzymatic ring-opening polymerization (ROP) is a benign method for preparing polyesters, such as polylactides and other polylactones. These reactions are typically carried out at relatively high temperatures (60–130 °C), however, there is a deficiency of enzyme-compatible solvents for such thermally-demanding biocatalytic processes. In this study, we have prepared a series of short-chained glycol-grafted ionic liquids (ILs) based on a phosphonium, imidazolium, pyridinium, ammonium, or piperidinium cationic headgroup. Most of these glycol-grafted ILs exhibit relatively low dynamic viscosities (33–123 mPa s at 30 °C), coupled with excellent short-term thermal stabilities with decomposition temperatures (T_dcp) in the 318–403 °C range. Significantly, the long-term thermal stability under conditions matching those for enzymatic ROP synthesis (130 °C for 7 days) is excellent for several of these task-specific ILs. Using Novozym 435-catalyzed ROP, these ILs are demonstrated to be viable solvents for the enzymatic production of reasonable yields (30–48%) of high molecular mass (M_w ∼20 kDa) poly(l-lactide) and poly(ε-caprolactone) compared to solventless conditions (12–14 kDa).

New glycol-functionalized ionic liquids exhibit high thermal stability and are lipase-compatible, leading to a high molecular weight of polyester in the enzymatic ring-opening polymerization reaction.     

Phosphorus pentoxide as a cost-effective,metal-free catalyst for ring opening polymerization of ε-caprolactone

The ring-opening polymerization (ROP) of ε-caprolactone (ε-CL) using phosphorus pentoxide (P₂O₅) as a metal-free catalyst and isopropanol (iPrOH) as initiator resulted in the preparation of poly(ε-caprolactone) with narrow weight distribution. NMR spectroscopy analyses of the prepared PCL indicated the presence of the initiator residue at the end of the polymer chain, implying the occurrence of the ε-CL-catalysis ROP through a monomer activation mechanism. Kinetic experiments confirmed the controlled/living nature of ε-CL ring-opening catalyzed by phosphorus pentoxide. The commercial availability of phosphorus pentoxide and its easy-handling provide additional opportunities for polymer synthesis and nanocomposite manufacturing.

The ring-opening polymerization (ROP) of ε-caprolactone (ε-CL) using phosphorus pentoxide (P₂O₅) as a metal-free catalyst and isopropanol (iPrOH) as initiator resulted in the preparation of poly(ε-caprolactone) with narrow weight distribution.     

High Tm linear poly(l-lactide)s prepared via alcohol-initiated ROPs of l-lactide

Alcohol-initiated ROPs of l-lactide were performed in bulk at 160 °C for 72 h with variation of the catalyst or with variation of the initiator (aliphatic alcohols). Spontaneous crystallization was only observed when cyclic Sn(ii) compounds were used as a catalyst. Regardless of initiator, high melting crystallites with melting temperatures (T_m) of 189–193 °C were obtained in almost all experiments with Sn(ii) 2,2′-dioxybiphenyl (SnBiph) as catalyst, even when the time was shortened to 24 h. These HT_m poly(lactide)s represent the thermodynamically most stable form of poly(l-lactide). Regardless of the reaction conditions, such high melting crystallites were never obtained when Sn(ii) 2-ethylhexanoate (SnOct₂) was used as catalyst. SAXS measurements evidenced that formation of HT_m poly(l-lactide) involves growth of the crystallite thickness, but chemical modification of the crystallite surface (smoothing) seems to be of greater importance. A hypothesis, why the “surface smoothing” is more effective for crystallites of linear chains than for crystallites composed of cycles is discussed.

By variation of reaction conditions and catalysts a cyclic tin(ii) compound was found, which enables synthesis of high melting (>190 °C) poly(l-lactide) via ROP of l-lactide, whereas the technically used catalyst SnOct₂ does not show such a performance.     

Branched-chain Amino Acid Nitrogen Transfer to Alanine In Vivo in Dogs: DIRECT ISOTOPIC DETERMINATION WITH [15N]LEUCINE

To investigate the contribution of branched-chain amino acids as a nitrogen source for alanine in vivo, dogs were infused with l-[¹⁵N]leucine, l-[U-¹⁴C]leucine, l-[2,3,3,3-²H₄]alanine, and d-[6,6-²H₂]-glucose. ¹⁴C and ¹⁵N isotopic equilibrium in plasma leucine, and deuterium enrichment in arterial and femoral plasma glucose and alanine were achieved within 3 h of initiation of the respective isotope infusion in all animals. The average flux of leucine determined by [¹⁵N]leucine was 5.4 μmol·kg⁻¹·min⁻¹, whereas using [¹⁴C]leucine it was 3.7 μmol·kg⁻¹·min⁻¹. Turnover rates for alanine and glucose were 11.0 and 17.2 μmol·kg⁻¹·min⁻¹, respectively.     

Ring opening polymerization of d,l-lactide and ε-caprolactone catalysed by (pyrazol-1-yl)copper(ii) carboxylate complexes

1,2-Bis{(3,5-dimethylpyrazol-1-yl)methyl}benzene (L) reacts with [Cu(OAc)₂] and C₆H₅COOH, 4-OH-C₆H₄COOH, 2-Cl-C₆H₄COOH and (3,5-NO₂)₂-C₆H₃COOH to afford the copper complexes [Cu₂(C₆H₅COO)₄(L)₂] (1), [Cu₂(4-OH-C₆H₄COO)₄(L)₂] (2), [Cu₂(2-Cl-C₆H₄COO)₄(L)₂]_n (3) and [Cu{(3,5-NO₂)₂-C₆H₃COO}₂L]_n (4) which are characterised by IR, mass spectrometry, elemental analyses, and X-ray crystallography. The structural data revealed two geometries that are adopted by the complexes: (i) paddle wheel in 1, 2·7H₂O, 3 and (ii) regular chains in 3 and 4. Magnetic studies show strong antiferromagnetic couplings in the paddle wheel complexes and a weak antiferromagnetic coupling in the monometallic chain one. Catalysis studies performed with these complexes (1–4) showed that they initiate ring opening polymerization (ROP) of ε-caprolactone (ε-CL) under solvent-free conditions and d,l-lactide in toluene at elevated temperatures. Polycaprolactone (PCL) and poly(d,l-lactide) (PLA) obtained from the polymerization reactions are of low molecular weights (858 for PCL and 602 Da for PLA for initiator 1) and polydispersity indices (typically 2.16 for PCL and 1.64 for PLA with 1 as the initiator). End group analysis of the polymers, determined by MALDI-ToF MS, indicates that the polymers have benzoate, hydroxyl, methoxy and cyclic end groups.

We report the synthesis, structure and complete characterization of four new pyrazolyl carboxylate-based copper(ii) complexes that catalyze the ring opening polymerization of ε-caprolactone under solvent-free conditions and of d,l-lactide in toluene.     

Efficiency of liquid tin(ii) n-alkoxide initiators in the ring-opening polymerization of l-lactide: kinetic studies by non-isothermal differential scanning calorimetry

Novel soluble liquid tin(ii) n-butoxide (Sn(OnC₄H₉)₂), tin(ii) n-hexoxide (Sn(OnC₆H₁₃)₂), and tin(ii) n-octoxide (Sn(OnC₈H₁₇)₂) initiators were synthesized for use as coordination–insertion initiators in the bulk ring-opening polymerization (ROP) of l-lactide (LLA). In order to compare their efficiencies with the more commonly used tin(ii) 2-ethylhexanoate (stannous octoate, Sn(Oct)₂) and conventional tin(ii) octoate/n-alcohol (SnOct₂/nROH) initiating systems, kinetic parameters derived from monomer conversion data were obtained from non-isothermal differential scanning calorimetry (DSC). In this work, the three non-isothermal DSC kinetic approaches including dynamic (Kissinger, Flynn–Wall, and Ozawa); isoconversional (Friedman, Kissinger–Akahira–Sunose (KAS) and Ozawa–Flynn–Wall (OFW)); and Borchardt and Daniels (B/D) methods of data analysis were compared. The kinetic results showed that, under the same conditions, the rate of polymerization for the 7 initiators/initiating systems was in the order of liquid Sn(OnC₄H₉)₂ > Sn(Oct)₂/nC₄H₉OH > Sn(Oct)₂ ≅ liquid Sn(OnC₆H₁₃)₂ > Sn(Oct)₂/nC₆H₁₃OH ≅ liquid Sn(OnC₈H₁₇)₂ > Sn(Oct)₂/nC₈H₁₇OH. The lowest activation energies (E_a = 52, 59, and 56 kJ mol⁻¹ for the Kissinger, Flynn–Wall, and Ozawa dynamic methods; E_a = 53–60, 55–58, and 60–62 kJ mol⁻¹ for the Friedman, KAS, and OFW isoconversional methods; and E_a = 76–84 kJ mol⁻¹ for the B/D) were found in the polymerizations using the novel liquid Sn(OnC₄H₉)₂ as the initiator, thereby showing it to be the most efficient initiator in the ROP of l-lactide.

The efficiency of homogeneous liquid tin(ii) n-alkoxide initiators in the ROP of l-lactide was reported in this work by non-isothermal DSC kinetic approaches.     

A novel catalytic kinetic method for the determination of mercury(ii) in water samples

Mercury(ii) ions act as catalyst in the substitution of cyanide ion in hexacyanoruthenate(ii) by pyrazine (Pz) in an acidic medium. This property of Hg(ii) has been utilized for its determination in aqueous solutions. The progress of reaction was followed spectrophotometrically by measuring the increase in absorbance of the yellow colour product, [Ru(CN)₅Pz]³⁻ at 370 nm (λ_max, ε = 4.2 × 10³ M⁻¹ s⁻¹) under the optimized reaction conditions; 5.0 × 10⁻⁵ M [Ru(CN)₆⁴⁻], 7.5 × 10⁻⁴ M [Pz], pH 4.00 ± 0.02, ionic strength (I) = 0.05 M (KCl) and temp. 45.0 ± 0.1 °C. The proposed method is based on the fixed time procedure under optimum reaction conditions. The linear regression (calibration) equations between the absorbance at fixed times (t = 15, 20 and 25 min) and [Hg(ii)] were established in the range of 1.0 to 30.0 × 10⁻⁶ M. The detection limit was found to be 1.5 × 10⁻⁷ M of Hg(ii). The effect of various foreign ions on the proposed method was also studied and discussed. The method was applied for the determination of Hg(ii) in different wastewater samples. The present method is simple, rapid and sensitive for the determination of Hg(ii) in trace amount in the environmental samples.

Mercury(ii) ions act as catalyst in the substitution of cyanide ion in hexacyanoruthenate(ii) by pyrazine (Pz) in an acidic medium.     

Antiproliferative activity of new pentacyclic triterpene and a saponin from Gladiolus segetum Ker-Gawl corms supported by molecular docking study

A new triterpenoidal saponin identified as 3-O-[β-d-glucopyranosyl-(1 → 2)-β-d-glucopyranosyl-(1 → 4)-β-d-xylopyranosyl]-2β,3β,16α-trihydroxyolean-12-en-23,28-dioic acid-28-O-α-l-rhamnopyranosyl-(1 → 4)-α-l-rhamnopyranosyl-(1 → 2)-β-d-glucopyranosyl-(1 → 2)-α-l-arabinopyranoside 1 together with a new oleanane triterpene identified as 2β,3β,13α,22α-tetrahydroxy olean-23,28-dioic acid 2 and 6 known compounds (3–8) have been isolated from Gladiolus segetum Ker-Gawl corms. The structural elucidation of the isolated compounds was confirmed using different chemical and spectroscopic methods, including 1D and 2D NMR experiments as well as HR-ESI-MS. Moreover, the in vitro cytotoxic activity of the fractions and that of the isolated compounds 1–8 were investigated against five human cancer cell lines (PC-3, A-549, HePG-2, MCF-7 and HCT-116) using doxorubicin as a reference drug. The results showed that the saponin fraction exhibited potent in vitro cytotoxic activity against the five human cancer cell lines, whereas the maximum activity was exhibited against the PC-3 and A-549 cell lines with the IC₅₀ values of 1.13 and 1.98 μg mL⁻¹, respectively. In addition, compound 1 exhibited potent activity against A-549 and PC-3 with the IC₅₀ values of 2.41 μg mL⁻¹ and 3.45 μg mL⁻¹, respectively. Interestingly, compound 2 showed the maximum activity against PC-3 with an IC₅₀ of 2.01 μg mL⁻¹. These biological results were in harmony with that of the molecular modeling study, which showed that the cytotoxic activity of compound 2 might occur through the inhibition of the HER-2 enzyme.

A new triterpenoidal saponin 1, a new oleanane triterpene 2, and 6 known compounds (3–8) have been isolated from Gladiolus segetum Ker-Gawl corms.     

Synthesis of alginate–polycation capsules of different composition: characterization and their adsorption for [As(iii)] and [As(v)] from aqueous solutions

The uptake of arsenite [As(iii)] and arsenate [As(v)] by functionalized calcium alginate (Ca-Alg) beads from aqueous solutions was investigated. Ca-Alg beads were protonated with poly-l-lysine (PLL) or polyethyleneimine (PEI) using 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide/N-hydroxysuccinimide (EDC/NHS) or glutaraldehyde (GA) as crosslinking agents. Four types of protonated beads were prepared: Ca-Alg-EDC/NHS (PLL or PEI) and Ca-Alg-GA (PLL or PEI). Fourier transform infrared spectroscopy in total attenuated reflection mode (FTIR-ATR), analysis showed presence and increased intensity of bands corresponding to OH, NH, CH₂ and CH₃ groups in modifications with both polycations. In addition, thermogravimetric analysis and atomic force microscopy of all modified capsules showed an increase in thermal stability and uniformity of the capsules, respectively. Ca-Alg-EDC/NHS-PLL beads had the maximum adsorption capacity of [As(v)] (312.9 ± 4.7 μg g⁻¹ of the alginate) at pH 7.0 and 15 minute exposure, while Ca-Alg-EDC/NHS-PEI beads had the maximum adsorption capacity of [As(iii)] (1052.1 ± 4.6 μg g⁻¹ of alginate). However, all these EDC containing beads were degraded in the presence of citrate. Ca-Alg-GA-PEI beads removed 252.8 ± 9.7 μg of [As(v)] μg g⁻¹ of alginate and 524.7 ± 5.3 de [As(iii)] μg g⁻¹ of alginate, resulting the most stable capsules and suitable for As removal.

A simple protonation of alginate beads allows the absorption of arsenate and arsenite.     

Tailor-made block copolymers of l-, d- and rac-lactides and ε-caprolactone via one-pot sequential ring opening polymerization by pyridylamidozinc(ii) catalysts

Three-coordinated Zn(ii) complexes bearing sterically encumbered bidentate monoanionic [N,N⁻] pyridylamido ligands efficiently catalyze the ring opening polymerization of lactide (LA) and ε-caprolactone (CL). Owing to the polymerization controlled nature and high rate, precise stereodiblock poly(LLA-b-DLA) with different block lengths can be easily produced by one-pot sequential monomer addition at room temperature in short reaction times. NMR, SEC and DSC analyses confirm the production of highly isotactic diblock copolymers which crystallize in the high melting stereocomplex phase. Stereo-triblock and tetrablock copolymers of l-LA, d-LA and rac-LA have been synthesized similarly. Finally, a diblock poly(CL-b-LA) has been easily obtained by sequential addition of ε-caprolactone and lactide under mild conditions.

New 3-coordinated Zn ROP catalysts afford lactide stereo-block copolymers with variable block lengths and steric structures and diblock ε-caprolactone-lactide copolymers at room temperature and in short reaction times.     

l-Menthol alleviates cigarette smoke extract induced lung injury in rats by inhibiting oxidative stress and inflammation via nuclear factor kappa B,p38 MAPK and Nrf2 signalling pathways

l-Menthol is the main ingredient of peppermint which affects various pharmacological effects such as anti-inflammation and anti-oxidative activity. In this study, we aimed to evaluate the potential effects of l-menthol on cigarette smoke extract (CSE) induced lung injury in rats. Morphology assessment results revealed that administration with l-menthol (5, 10 or 20 mg kg⁻¹ d⁻¹) significantly alleviated CSE-induced lung injury. Besides, l-menthol significantly reduced the inflammatory response by suppressing the production of tumor necrosis factor-α (TNF-α), interleukin-1β (IL-1β) and interleukin-6 (IL-6) via downregulating nuclear factor kappa B (NF-κB) and p38 MAPK pathways. Meanwhile, l-menthol decreased the levels of oxidative stress markers including malondialdehyde (MDA) and myeloperoxidase (MPO) whereas it increased the amount of glutathione (GSH), glutathione peroxidase (GSH-Px), superoxide dismutase (SOD) and total antioxidant capacity (T-AOC) through activation of the Nrf2 pathway. Furthermore, the expression of MMP-9 and TIMP-1 in lungs was reduced after treatment with l-menthol, and this indicated that l-menthol might have a potential effect on airway remodeling. Moreover, immunohistochemistry analyses indicated that l-menthol could suppress the infiltration of CD4⁺ and CD8⁺ T cells in lung tissues and this was probably due to the immune regulation activity of l-menthol. Taken together, our findings support that l-menthol might be a potential candidate for the treatment of CSE-induced lung injury in rats.

l-Menthol is the main ingredient of peppermint which affects various pharmacological effects such as anti-inflammation and anti-oxidative activity.     

Structural analysis and antioxidant activity of an arabinoxylan from Malvastrum coromandelianum L. (Garcke)

Malvastrum coromandelianum L. (Garcke) is extensively used in traditional medicinal systems to treat various ailments. In the present study, an alkali-soluble polysaccharide (MAP) was isolated from the leaves of M. coromandelianum in 1.15% (w/w) yield. MAP was composed of l-rhamnose, l-arabinose, d-xylose, d-glucose and d-galactose in a 1.00 : 6.04 : 19.88 : 1.07 : 3.03 molar ratio along with d-glucuronic acid (1.95). Methylation/linkage analysis revealed a backbone of →4)-β-d-Xylp(1→ (30.09 mol%) with a side chain of →3)-α-l-Araf(1→ (15.21 mol%) residues. The structure of MAP was elucidated by a combination of degradative and derivatization techniques, including hydrolysis, alditol acetate derivatization, methylation, GC-MS, partial hydrolysis, ESI-MS and NMR (1D, 2D) spectral analysis. Based on correlation analysis, MAP was found to be an arabinoxylan comprising a backbone of →4)-β-d-linked Xylp(1→ with branching at O-2 by a →3)-α-l-Araf(1→ and →3)-β-d-Xylp(1→ chain. MAP also exhibited ferric ion reducing activity, with a reducing power of 0.914 ± 0.01 (R² = 0.972) at 1 mg mL⁻¹ concentration, which showed dose-dependent behavior. MAP can be utilized as a potential antioxidant.

The structure of MAP was studied by degradative, derivatization and spectroscopic methods, and it was found to be an arabinoxylan comprising a backbone of →4)-β-d-linked Xylp(1→ with branching at O-2 by →3)-α-l-Araf(1→ and →3)-β-d-Xylp(1→ chains.     

Anti-Hepatitis B Virus Activity and Metabolism of 2′,3′-Dideoxy-2′,3′-Didehydro-β-l(?)-5-Fluorocytidine

2′,3′-Dideoxy-2′,3′-didehydro-β-l(−)-5-fluorocytidine [l(−)Fd4C] was found to be at least 10 times more potent than β-l-2′,3′-dideoxy-3′-thiacytidine [l(−)SddC; also called 3TC, or lamivudine]against hepatitis B virus (HBV) in culture. Its cytotoxicity against HepG2 growth in culture was also greater than that of l(−)SddC (3TC). There was no activity of this compound against mitochondrial DNA synthesis in cells at concentrations up to 10 μM. The dynamics of recovery of virus from the medium of cells pretreated with equal drug concentrations were slower with l(−)Fd4C than with l(−)SddC (3TC). l(−)Fd4C could be metabolized to mono-, di-, and triphosphate forms. The degree of l(−)Fd4C phosphorylation to the 5′-triphosphate metabolite was higher than the degree of l(−)SddC (3TC) phosphorylation when equal extracellular concentrations of the two drugs were used. The apparent K_m of l(−)Fd4C phosphorylated metabolites formed intracellularly was higher than that for l(−)SddC (3TC). This may be due in part to a difference in the behavior of l(−)Fd4C and l(−)SddC (3TC) towards cytosolic deoxycytidine kinase. Furthermore, l(−)Fd4C 5′-triphosphate was retained longer within cells than l(−)SddC (3TC) 5′-triphosphate. l(−)Fd4C 5′-triphosphate inhibited HBV DNA polymerase in competition with dCTP with a K_i of 0.069 ± 0.015 μM. Given the antiviral potency and unique pharmacodynamic properties of l(−)Fd4C, this compound should be considered for development as an expanded-spectrum anti-HBV drug.Hepatitis B virus (HBV) infection is one of the most serious health issues in the world today (1, 3). β-l(−)-2′,3′-Dideoxy-3′-thiacytidine [l(−)SddC; also called 3TC, or lamivudine] (Fig. ​(Fig.1)1) is the first β-l(−) nucleoside analog identified by us and others to have potent activity against HBV in culture (4, 8, 12, 17). This drug exerts its action by inhibiting HBV DNA synthesis due to the preferential interaction of the l(−)SddC (3TC) 5′-triphosphate metabolite with HBV DNA polymerase (4). Unlike dideoxycytidine (ddC, or zalcitabine), a β-d(+) nucleoside analog with the natural nucleoside conformation in DNA and RNA, l(−)SddC (3TC) does not have potent activity against mitochondrial DNA (mtDNA) synthesis, which is important for maintaining the function of cells (4). Clinical trials of l(−)SddC (3TC) for the treatment of chronic HBV infection are ongoing and look promising (2, 7, 13, 16, 18, 19). Its potential value for HBV-infected patients undergoing liver transplantation is also being evaluated, since l(−)SddC (3TC) can suppress HBV DNA serum levels in these patients. However, apparent l(−)SddC (3TC)-resistant HBV emerged in some patients upon long-term treatment (13, 16, 18). The HBV-resistant genotype appears to be associated with the mutation of methionine to valine or isoleucine in the YMDD motif of HBV DNA polymerase (13, 16, 18). This mutation was previously demonstrated and could render duck HBV resistant to l(−)SddC (3TC) (11). It is not clear if this mutation alone can lead to resistance and, if so, to what degree HBV resistance to l(−)SddC (3TC) develops. Open in a separate windowFIG. 1Structures of l(−)deoxycytidine analogs.One approach to overcoming clinical drug resistance is to use higher dosages of l(−)SddC (3TC) given the therapeutic index of the compound in vitro. However, the potency of l(−)SddC (3TC) against HBV in the clinic could be a limiting factor given the dosage application. The antiviral potency is determined not only by its antiviral activity but also by the pharmacodynamic nature of its active metabolite, l(−)SddC (3TC) 5′-triphosphate, in vivo. A more potent compound with more favorable pharmacodynamic behavior of intracellularly active metabolites would be worth exploring.In the studies reported herein, we describe the anti-HBV activity, metabolism, and pharmacodynamic properties of 2′,3′-dideoxy-2′,3′-didehydro-β-l(−)-5-fluorocytidine [l(−)Fd4C](Fig. 1) in comparison with those of l(−)SddC (3TC), including its behavior toward deoxycytidine kinase and the interaction of l(−)Fd4C 5′-triphosphate with virion-associated HBV DNA polymerase. Preliminary studies of the anti-HBV and anti-human immunodeficiency virus (HIV) activities of l(−)Fd4C were previously reported by us and others (10, 15).     

Ratiometric fluorescence sensing of d-allulose using an inclusion complex of γ-cyclodextrin with a benzoxaborole-based probe

Because d-allulose has been attracting attention as a zero-calorie sugar, the selective sensing of d-allulose is desired to investigate its health benefits. We report herein a novel fluorescence chemosensor that is based on an inclusion complex of γ-cyclodextrin (γ-CyD) with a benzoxaborole-based probe. Two inclusion complexes, 1/γCyD and 2/γCyD, were prepared by mixing γ-CyD with their corresponding probes in a water-rich solvent, where γ-CyD encapsulates two molecules of the probes inside its cavity to form a pyrene dimer. Both 1/γCyD and 2/γCyD exhibit monomeric and dimeric fluorescence from the pyrene moieties. By the reaction of 1/γCyD with saccharides, the intensities of monomeric and dimeric fluorescence remained unchanged and decreased, respectively. We have demonstrated that 1/γCyD has much higher affinity for d-allulose than for the other saccharides (d-fructose, d-glucose, and d-galactose). The conditional equilibrium constants for the reaction systems were determined to be 498 ± 35 M⁻¹ for d-fructose, 48.4 ± 25.3 M⁻¹ for d-glucose, 15.0 ± 3.3 M⁻¹ for d-galactose, and (8.05 ± 0.59) × 10³ M⁻¹ for d-allulose. These features of 1/γCyD enable ratiometric fluorescence sensing with high sensitivity and selectivity for d-allulose. The limits of detection and quantification of 1/γCyD for d-allulose at pH 8.0 were determined to be 6.9 and 21 μM, respectively. Induced circular dichroism spectral study has shown that the reaction of 1/γCyD with d-allulose causes the monomerisation of the dimer of probe 1 that is encapsulated by γ-CyD, which leads to the diminishment of the dimeric fluorescence.

We proposed an inclusion complex of γ-cyclodextrin with a benzoxaborole-based fluorescent probe as a highly sensitive and selective chemosensor for d-allulose.     

Structure characterization and anticoagulant activity of a novel polysaccharide from Leonurus artemisia (Laur.) S. Y. Hu F

An acidic polysaccharide, named LAP-1, was extracted and isolated from Leonurus artemisia (Laur.), and was further purified with ion exchange chromatography and gel chromatography. The extraction conditions of the crude polysaccharides were optimized by single-factor experiments and response surface methodology. The primary structure of the purified polysaccharide was measured by FT-IR, GC-MS, and NMR. The results showed that LAP-1 was mainly composed of galacturonic acid (GalA), mannose (Man), xylose (Xyl), rhamnose (Rha), arabinose (Ara), glucose (Glc), galactose (Gal), fucose (Fuc), ribose (Rib), and glucuronic acid (GlcA) in the molar ratio of 8.74 : 3.45 : 1.02 : 1 : 2.11 : 5.60 : 4.73 : 1.08 : 1.09 : 1.47. Primary structure analysis results indicated that LAP-1 contained characteristic glycosyl linkages such as →1)-α-d-Manp, →1)-α-d-Glcp, →1)-α-d-Arap-(2→, →1)-β-d-Galp-(3→, →1)-β-d-Manp-(4→, →1)-β-d-Galp-(4→, →1)-β-d-Glcp-(4→, →1)-β-d-GalAp-(4→, →1)-β-d-GlcAp-(4→, →1)-β-d-Manp-(4,6→, →1)-β-d-Manp-(3,4→. The M_w/M_n (PDI), M_n, M_z and M_w of LAP-1 were determined to be 1.423, 6.979 × 10³ g mol⁻¹, 1.409 × 10⁴ g mol⁻¹, and 9.930 × 10³ g mol⁻¹ by HPSEC-MALLS-RID and DLS. SEM, TEM and AFM results indicated that LAP-1 was a highly branched structure. LAP-1 showed mild anticoagulant activity, low toxicity, and less spontaneous bleeding compared with heparin sodium. These results demonstrated the effective coagulation activity of Leonurus artemisia polysaccharides. Thus, the purified LAP-1 could be explored as a promising anticoagulant agent for the treatment of coagulation disorders.

An acidic polysaccharide, denoted LAP-1 was extracted, isolated and purified from Leonurus artemisia (Laur.), in addition to its structure and anticoagulant activity were explored.     

Presence of δ-(l-α-Aminoadipyl)-l-Cysteinyl-d-Valine in Fermentations of Penicillium chrysogenum

Cultures of Penicillium chrysogenum, growth with [³⁵S]sulfate or labeled amino acids, were examined by ion-exchange chromatography for possible peptidic precursors of penicillin. A sulfur-containing compound, present in both the mycelial extracts and the culture filtrates, was eluted at the location of the synthetic lld-tripeptide δ-(l-α-aminoadipyl)-l-cysteinyl-d-valine. Since this compound was also labeled when the cultures were incubated with dl-[6-¹⁴C]α-aminoadipic acid, l-[3,3′-³H]cystine, or dl-[1-¹⁴C]valine, its identity with the synthetic lld-tripeptide can be accepted. No δ-(l-α-aminoadipyl)-l-cysteine or lll-tripeptide were detected. The implications of these findings for tripeptide and penicillin biosynthesis are discussed.