Study on the Selectivity of Benzoylation of Metal Chelates of Sucrose1

Abstract

A study of the selectivity of metal chelate-directed benzoylation of sucrose dianion, relative to unchelated sucrose anion, was conducted as part of a study on new synthetic approaches to the high-potency sweetener sucralose. Ionic complexes of sucrose with various metal ions were prepared in DMF and the resulting complexes reacted at low temperature with benzoic anhydride. Cobalt and manganese salts directed esterification mostly to the 3′-OH on the fructosyl portion. Unchelated sucrose anion and other metals favored esterification at the 2-OH of the glucosyl portion. Migration of the benzoate ester along the glucose portion was observed in the direction O-2 to O-6 at moderate temperature, but at higher temperature transannular migration was observed from the glucose to the fructose ring. Reaction mixtures were analyzed by HPLC and monobenzoates identified by retention times relative to standards. Six of eight possible monobenzoates of sucrose were isolated from mixtures and identified by their ¹H NMR spectra.     

Aggregation Effects in Visible‐Light Flavin Photocatalysts: Synthesis,Structure, and Catalytic Activity of 10‐Arylflavins

A series of 10‐arylflavins (10‐phenyl‐, 10‐(2′,6′‐dimethylphenyl)‐, 10‐(2′,6′‐diethylphenyl)‐, 10‐(2′,6′‐diisopropylphenyl)‐, 10‐(2′‐tert‐butylphenyl)‐, and 10‐(2′,6′‐dimethylphenyl)‐3‐methylisoalloxazine ( 2 a – f )) was prepared as potentially nonaggregating flavin photocatalysts. The investigation of their structures in the crystalline phase combined with ¹H‐DOSY NMR spectroscopic experiments in CD₃CN, CD₃CN/D₂O (1:1), and D₂O confirm the decreased ability of 10‐arylflavins 2 to form aggregates relative to tetra‐O‐acetyl riboflavin ( 1 ). 10‐Arylflavins 2 a – d do not interact by π–π interactions, which are restricted by the 10‐phenyl ring oriented perpendicularly to the isoalloxazine skeleton. On the other hand, N3? H???O hydrogen bonds were detected in their crystal structures. In the structure of 10‐aryl‐3‐methylflavin ( 2 f ) with a substituted N3 position, weak C? H???O bonds and weak π–π interactions were found. 10‐Arylflavins 2 were tested as photoredox catalysts for the aerial oxidation of 4‐methoxybenzyl alcohol to the corresponding aldehyde (model reaction), thus showing higher efficiency relative to 1 . The quantum yields of 4‐methoxybenzyl alcohol oxidation reactions mediated by arylflavins 2 were higher by almost one order of magnitude relative to values in the presence of 1 .     

A Resin‐Linker‐Vector Approach to Radiopharmaceuticals Containing 18F: Application in the Synthesis of O‐(2‐[18F]‐Fluoroethyl)‐L‐tyrosine

A Resin‐linker‐vector (RLV) strategy is described for the radiosynthesis of tracer molecules containing the radionuclide ¹⁸F, which releases the labelled vector into solution upon nucleophilic substitution of a polystyrene‐bound arylsulfonate linker with [¹⁸F]‐fluoride ion. Three model linker‐vector molecules 7 a – c containing different alkyl spacer groups were assembled in solution from (4‐chlorosulfonylphenyl)alkanoate esters, exploiting a lipase‐catalysed chemoselective carboxylic ester hydrolysis in the presence of the sulfonate ester as a key step. The linker‐vector systems were attached to aminomethyl polystyrene resin through amide bond formation to give RLVs 8 a – c with acetate, butyrate and hexanoate spacers, which were characterised by using magic‐angle spinning (MAS) NMR spectroscopy. On fluoridolysis, the RLVs 8 a , b containing the longer spacers were shown to be more effective in the release of the fluorinated model vector (4‐fluorobutyl)phenylcarbamic acid tert‐butyl ester ( 9 ) in NMR kinetic studies and gave superior radiochemical yields (RCY≈60 %) of the ¹⁸F‐labelled vector. The approach was applied to the synthesis of the radiopharmaceutical O‐(2‐[¹⁸F]‐fluoroethyl)‐L ‐tyrosine ([¹⁸F]‐FET), delivering protected [¹⁸F]‐FET in >90 % RCY. Acid deprotection gave [¹⁸F]‐FET in an overall RCY of 41 % from the RLV.     

Synthesis and Characterisation of Bismuth(III) Aminoarenesulfonate Complexes and Their Powerful Bactericidal Activity against Helicobacter pylori

The synthesis and characterisation of nine new tris‐substituted bismuth(III) aminoarenesulfonates of the general formula [Bi(O₃S‐R^N)₃] (R^N=o‐aminophenyl 1 , m‐aminophenyl 2 , 6‐amino‐3‐methoxyphenyl 3 , p‐aminophenyl 4 , 2‐pyridyl 5 , o‐aminonaphthyl 6 , 5‐aminonaphthyl 7 , 4‐amino‐3‐hydroxynaphthyl 8 and 5‐isoquinolinyl 9 ) is described. Two synthetic strategies, using Ag₂O and [Bi(OtBu)₃], were explored and compared. The possibility to access heteroleptic bismuth(III) complexes with the new silver(I) metathesis reaction is demonstrated with the synthesis of the heteroleptic bismuth(III) aminoarenesulfonate complexes [PhBi(O₃S‐P2)₂(dmso)] 10 , [Ph₂Bi(O₃S‐P2)]_∞ 11 and [PhBi(O₃S‐P2)₂]_∞ 12 , of which the solid state structures 10 and 12 are presented (2P‐SO₃^?=2‐pyridinesulfonate). These complexes offer remarkable in‐vitro activity against three standard laboratory strains of Helicobacter pylori (H. pylori) as demonstrated by their exceptionally low minimum inhibitory concentration (MIC) values of 0.049 μg mL^?1 for the strains 251 and B128, which places most MIC values in the nano‐molar region. These results demonstrate the importance of the amino functionality in addition to the sulfonate group on the bactericidal properties against H. pylori.     

Surface modification of cellulose nanocrystal with chitosan oligosaccharide for drug delivery applications

A novel drug delivery system based on two of the most abundant natural biopolymers was developed by modifying the surface of oxidized cellulose nanocrystal (CNC) with chitosan oligosaccharide (CS_OS). First, the primary alcohol moieties of CNC were selectively oxidized to carboxyl groups using the 2,2,6,6-tetramethylpiperidine-1-oxyl radical catalyst. The amino groups of CS_OS were then reacted with carboxylic acid groups on oxidized CNC (CNC-OX) via the carbodiimide reaction using N-hydroxysuccinimide and 1-ethyl-3-(3-dimethylaminopropyl)-carbodiimide as coupling agents. Successful grafting of CS_OS to CNC-OX was confirmed by infrared spectroscopy, thermogravimetry, potentiometric titration, and zeta potential measurements. The grafting resulted in a conversion of ~90 % carboxyl groups on CNC-OX and the degree of substitution was 0.26. CNC–CS_OS nanoparticles showed a binding efficiency of 21.5 % and a drug loading of 14 % w/w. A drug selective electrode was used to directly measure the concentration of procaine hydrochloride released from CNC–CS_OS particles. The in vitro drug release was studied at pH 8 and the nanoparticles revealed a fast release of up to 1 h, which can be used as biocompatible and biodegradable drug carriers for transdermal delivery applications.     

The BIOREMA project—part 3: International interlaboratory comparison for bio-ethanol test methods

The main objective of the reference materials for biofuel specifications (BIOREMA) project is the development of two test materials (one bio-ethanol material and one biodiesel material) with well-established reference values. Of a series of three papers, this part describes the material preparation, homogeneity study, stability study, and characterisation of the bio-ethanol material. The test material thus obtained was used in an interlaboratory comparison (ILC) to assess current practices and comparability amongst laboratories providing bio-ethanol testing services. Only 13 participants provided data, resulting in a small dataset for evaluation. Further, it appeared that for a number of laboratories, there was not sufficient material for the determination of all requested parameters. In most cases, as far as the data permit, it can be concluded that the consensus values (based on participant’s results) are in good agreement with the reference or the BIOREMA values (obtained by NMIs participating in the project). For three parameters, namely ethanol content, water content, and density, there is good agreement between the reference and consensus values. For these parameters, the reproducibility standard deviation is close to, or even smaller than, the expanded uncertainty associated with the reference value. A number of parameters show very poor reproducibility, for example, pH_e, electrolytic conductivity, and acidity. The same applies to sodium and copper content, which are very low and therefore challenging parameters to measure accurately. The results of the ILC underpin the need for certified reference materials and demonstrate the requirement for more robust quality control to improve the precision and trueness of the results from testing laboratories.     

Hemostatic efficacy and tissue reaction of oxidized regenerated cellulose hemostats

Oxidized regenerated cellulose (ORC) has been used as an absorbable hemostat since World War II. In the present study, hemostasis time was determined in a spleen incision model in swine. The effect of mass on absorbable hemostat efficacy and hemostasis time was evaluated by standardizing the ORC materials on a mass basis. The median hemostasis time for a single layer of the new nonwoven ORC was as much as 51 % shorter than woven ORC (P < 0.001). The mean hemostasis time for nonwoven ORC was not affected by the mass of hemostat applied to the wound. The hemostatic efficacy of woven ORC increased with the mass (layers) of hemostat applied to the wound. Nonwoven ORC is significantly faster in achieving hemostasis than woven ORC, and its hemostatic efficacy is not influenced by the mass of material applied. Tissue reaction was minimal and the material was fully absorbed by 14 days.     

On string topology of classifying spaces

Let G be a compact Lie group. By work of Chataur and Menichi, the homology of the space of free loops in the classifying space of G is known to be the value on the circle in a homological conformal field theory. This means in particular that it admits operations parameterized by homology classes of classifying spaces of diffeomorphism groups of surfaces. Here we present a radical extension of this result, giving a new construction in which diffeomorphisms are replaced with homotopy equivalences, and surfaces with boundary are replaced with arbitrary spaces homotopy equivalent to finite graphs. The result is a novel kind of field theory which is related to both the diffeomorphism groups of surfaces and the automorphism groups of free groups with boundaries. Our work shows that the algebraic structures in string topology of classifying spaces can be brought into line with, and in fact far exceed, those available in string topology of manifolds. For simplicity, we restrict to the characteristic 2 case. The generalization to arbitrary characteristic will be addressed in a subsequent paper.