Far ultraviolet optical rotatory properties of poly-L-tryptophan. I

A block copolymer [γ-Et-DL -Glu]_m [L -Trp]_n was prepared using N-carboxy anhydrides (NCA) of L -tryptohan and γ-ethyl DL -glutamate. The block copolymer, dissolved in trifluoroethanol (TFE)–dichloroacetic acid (DCA) mixtures, exhibited a sharp change in the specific rotation at 546 mμ when the solvent composition reached 70–75% DCA content. Optical rotatory dispersion (ORD) and circular dichroism (CD) measurement were carried out in TFE solution in the spectral range 180–350 mμ. Indole side-chain chromophores were found to be optically active in the polymer. On the other hand, these groups exhibit very small optical activity in the model compound C₆H₃? CH₂? O? CO? (L -Trp)₂? O? CH₃. Indole groups therefore appear to be in a dissymmetric environment only in the polymer. From these data it was concluded that poly-L -Trp is in some type of helical conformation in TFE. Strong overlapping of CD bands from side-chain chromophores and peptides chromophores in the wavelength range 185–240 mμ does not allow definite conclusions to be drawn about the type of helical conformation which exists in poly-L -Trp in TFE solution.     

Far-ultraviolet optical activity of saccharide derivatives. II. Dextran,amylose, and mycodextran acetes; dextran and amylose xanthates

The ultraviolet ORD and CD spectra of amylose, dextran, and mycodextran acetates and some of thier oligomers were recorded in trifluoroethanol solution in the 300–185nm wavelength range. Similarly, the spectra of amylose and dextran xanthates in water solution were obtained in the 400–200 nm range. In the amylose acetate series, the monomer and dimer both show a normal acetyl n → π* transition in CD, while the trimer and the polymer both exhibit an additional, shorter wavelength peak. The latter is presumed to arise from a helical conformation of the amylose chain. This interpretation is substantiated by a helix–coil type transition of the CD spectra of amylose triacetate at elevated temperatures and a reversion of the anomalous CD to the normal CD upon partial deacetylation. By contrast, neither dextran acetates nor mycodextran acetate exhibit any conformational effects. The CD of dextran acetates is quite sensitive to β-1,6 and branch linkages. The ORD and CD of amylose xanthate are complex, suggesting the presence of organized structure in solution. The dextran xanthate shows only a simple ORD spectrum and no observable CD.     

Location of proline derivatives in conformational space. I. Conformational calculations; optical activity and NMR experiments

In order to develop methods of analysis applicable to the determination of the conformation of biological polymers in solution, a series of proline derivatives was studied. The steric constraints of the pyrrolidine ring limit these compounds to a relatively small set of conformations. This set was further reduced by eliminating conformations with large computed conformational energy. Computations revealed that the conformational energy of the proline derivatives fits into one of three classes, depending on the bulk and the polarity of the C-terminal group. Three analogous classes of optical activity were observed. The optical activity data were analyzed in terms of conformations computed to be of low energy. In some cases qualitative theoretical considerations enabled molecular groups to be located. For example, solvent-dependent isomerization of the carboxyl hydrogen of N-acetyl-L -proline was detected. Nuclear magnetic resonance provided an experimental measure of the fraction of molecules which had cis unsymmetrically-substituted tertiary amide groups. This information aided and confirmed the other measures of molecular conformation.     

Location of proline derivatives in conformational space. II. Theoretical optical activity

The coupling of theoretical optical calculations with experimental data provides a check of the validity of the theory or provides conformational information. The theory was validated by studies in which the approximate conformation was located independently. These studies have shown that a theory restricted to the two lowest energy transitions for each chromophore gives qualitative agreement with experiment. On the other hand, for some of the proline derivatives, the theoretical treatment allows detailed conformational assignments. Both successes and failures in correlating theory with experiment are discussed. The results presented provide a basis for assessing the prospects for relating protein and polypeptide optical activity to their conformations.     

Synthesis and antibacterial activity of O-substituted nocathiacin I derivatives

The synthesis and antibacterial activity of a series of new nocathiacin I derivatives (1-12) containing polar water solubilizing groups is described. Most of these compounds exhibited potent antibacterial activity and have improved water solubility. In addition, compounds 5, 7-9 also exhibited potent in vivo activity.     

Synthesis and antimicrobial activity of new adamantane derivatives I

A series of fourteen derivatives of adamantane was synthesised. The new compound 4-(adamant-1-ylmethoxycarbonyl)phthalanhydride obtained from 1-adamantane-methanol and trimellitic anhydride chloride appeared very useful for preparation of a number of N-substituted phthalimides. Antimicrobial activity of the newly obtained derivatives such as, for example, 4-(adamant-1-ylmethoxycarbonyl)-N-(5-carboxypentamethylene)p hthalimide or 4-(adamant-1-ylmethoxycarbonyl)-N-(L-alanyl)phthalimide was tested against Staphylococcus aureus, Bacillus sp., Micrococcus flavus and Enterococcus faecium. The minimal inhibitory concentration (MIC) for these compounds against S. aureus were 0.022 and 0.05 microg/ml, respectively.     

Utilization of sugarcane bagasse cellulose for producing cellulose acetates: Novel use of residual hemicellulose as plasticizer

Sugarcane bagasse was fractionated to cellulose, hemicellulose and lignin by a proprietary steam explosion process, followed by downstream purifications, developed in our laboratory. The fractionated cellulose contained ～94% cellulose, about ～5% hemicellulose, traces of lignin (～0.2%), and ～1% ash. The cellulose was acetylated under heterogeneous conditions to obtain cellulose acetates. These were extensively characterized using FTIR, TGA, DSC, GPC, HPIC, WAXRD, and viscometry. The novel feature of this study was the utilization of the hemicellulose content (5%) of bagasse cellulose as an internal plasticizer. Through kinetic experimentation, we have demonstrated that the residual hemicellulose need not be considered as an impurity; rather it can be used in acetylated form as a plasticizer as well as a biodegradable additive for cellulose acetates made from slightly impure cellulose produced from non-wood origin. Our results therefore show how lignocellulosic agricultural wastes can be utilized to produce high value plastics.     

Regioselective deacetylation of cellulose acetates by acetyl xylan esterases of different CE-families

Cellulose acetate (CA) was found to be a substrate of several acetyl xylan esterases (AXE). Eight AXE from different carbohydrate esterase (CE) families were tested on their activity against CA with a degree of substitution of 0.7 and 1.4. The classification of the AXEs into CE families according to their structure by hydrophobic cluster analysis followed clearly their activity against CA. Within the same CE family similar, and between the CE families different deacetylation behaviours could be observed. Furthermore, each esterase family showed a distinct regioselective mode of action. The CE 1 family enzymes regioselectively cleaved the substituents in C2- and C3-position, while CE 5 family enzymes only cleaved the acetyl groups in C2-position. CE 4 family enzymes seemed to interact only with the substituents in C3-position. Evidence was found that the deacetylation reaction of the CE 1 family enzymes proceeded faster in C2- than in C3-position of CA. The enzymes were able to cleave acetyl groups from fully substituted anhydroglucose units.     

Synthesis of cellulose adipate derivatives

Cellulose esters containing adipates and other ester groups are synthesized by the reaction of commercially available cellulose esters in solution with the benzyl monoester of adipoyl chloride. The products, cellulose adipate esters in which the distal end of the adipate moiety is a benzyl ester, were easily converted to cellulose adipate derivatives by Pd-catalyzed hydrogenation. These cellulose adipate derivatives are promising biopolymers for drug delivery and other applications in which water-dispersion or swelling are desired.     

New cellulose sulfate derivatives and applications

The preparation of water-soluble cellulose sulfates having a degree of substitution (d.s.) of 0.3–2.0 by a homogeneous method is reported. Instead of sulfating cellulose directly, a reactive intermediate, namely, cellulose nitrite, was used, thereby permitting sulfation to proceed under homogeneous conditions. Products obtainable via the homogeneous method differ substantially from those prepared via the heterogeneous method used at present for the production of water-soluble cellulose derivatives. Principal chemical differences are the uniform distribution of the substituents, the exceptionally high molecular weight of the sulfate esters, and in the location of the substituents on the glucosyl residues. The differences result in a number of chemical and physical properties that are unique and not exhibited by other cellulose derivatives. Performance in application areas, such as oil recovery, paints, paper, textiles, cosmetics, and the like, is indicated by these properties.     

Biological activity and pharmacological prospects of lupane terpenoids: I. Natural lupane derivatives

The biological activity of natural and semisynthetic lupane triterpenoids is discussed in a two-part review. The first part is devoted to the pharmacological properties of natural lupane triterpenoids. Betulinic acid has proven to be the most effective antitumor agent among more than fifty natural lupanes.     

Biological activity and pharmacological prospects of lupane terpenoids: I. natural lupane derivatives

The biological activity of natural and semisynthetic lupane triterpenoids is discussed in a two-part review. The first part is devoted to the pharmacological properties of natural lupane triterpenoids. Betulinic acid has proven to be the most effective antitumor agent among more than fifty natural lupanes.     

Novel cellulose derivatives. Part VI. Preparation and thermal analysis of two novel cellulose esters with fluorine-containing substituents

Two novel cellulose esters were prepared with fluorine (F)-containing substituents using homogeneous phase reaction chemistry in DMAc/LiCl. The partially substituted derivatives and their corresponding perpropionates proved to be thermoplastic polymers. The 2,2-difluoroethoxy and 2,2,3,3,4,4,5,5-octafluoropentoxy substituents were easily identified by ¹H- and ¹⁹F-NMR spectroscopy without disclosing their precise location on the anhydroglucose unit. Thermal analysis revealed modest or no crystallinity; glass transition temperatures between 53 and 113°C; and improved thermal stability as compared to their F-free counterparts.     

Estimation of Cellobiohydrolase Ⅰ Activity by Numerical Differentiation of Dynamic Ultraviolet Spectroscopy

1,4-β-D-glucan cellobiohydrolase Ⅰ （CBH Ⅰ）, p-nitrophenyl β-D-cellobioside, p-nitrophenol and cellobiose show distinct ultraviolet spectra, allowing the design of an assay to track the dynamic process of p-nitrophenyl β-D-cellobioside hydrolysis by CBH Ⅰ. Based on the linear relationship between p-nitrophenol formation in the hydrolysate and its first derivative absorption curve of AUC340-400 m （area under the curve）, a new sensitive assay for the determination of CBH Ⅰ activity was developed. The dynamic parameters of catalysis reaction, such as Vm and kcat, can all be derived from this result. The influence of β-glucosidase and endoglucanase in crude enzyme sample on the assay was discussed in detail. This approach is useful for accurate determination of the activity of CBHs.     

Antiviral activity of benzimidazole derivatives. II. Antiviral activity of 2-phenylbenzimidazole derivatives

Seventy-six 2-phenylbenzimidazole derivatives were synthesized and evaluated in cell-based assays for cytotoxicity and antiviral activity against a panel of 10 RNA and DNA viruses. The most commonly affected viruses were, in decreasing order, CVB-2, BVDV, Sb-1, HSV-1, and YFV, while HIV-1 and VSV were not affected, and RSV, VV and Reo-1 were only susceptible to a few compounds. Thirty-nine compounds exhibited high activity (EC₅₀ = 0.1–10 μM) against at least one virus, and four of them were outstanding for their high and selective activity against VV (24, EC₅₀ = 0.1 μM) and BVDV (50, 51, and 53 with EC₅₀ = 1.5, 0.8, and 1.0 μM, respectively). The last compounds inhibited at low micromolar concentrations the NS5B RdRp of BVDV and also of HCV, the latter sharing structural similarity with the former. The considered compounds represent attractive leads for the development of antiviral agents against poxviruses, pestiviruses and even HCV, which are important human and veterinary pathogens.