Krasimira T. Petrova

Library of mild and economic protocols for the selective derivatization of sucrose under microwave irradiation

The chemistry of sucrose is very challenging due to its eight hydroxyl groups, three of which are primary, with very similar reactivities, thus control of the chemoselectivity is a central issue. In this work, the selective formation of monounsaturated esters at the 6-position, by applying the Mitsunobu conditions for the selective esterification of sucrose, is reported. Also, the outcome of a number of mono-substitution reactions at positions 6 or 6′, and di-substitution reactions at positions 6 and 6′ have been explored. Mild and energy-efficient procedures, with short reaction times (5 to 10 min) using microwave irradiation have been developed, and the results compared with conventional procedures. In some cases, the use of microwave irradiation appeared to provide not only time saving but also improved selectivity.

Novel Unsaturated Sucrose Ethers and Their Application as Monomers

Novel unsaturated ethers were synthesised in good yields starting from sucrose, using a two-step mild and efficient procedure based on the Gassman method, which consists in forming a vinyl group by the elimination of ethanol from mixed acetals with trimethylsilyl trifluoromethanesulfonate in the presence of alkyl amines. Mixed acetals are readily obtained from the corresponding alcohols and ethyl vinyl ether, using an acidic catalyst. Conventional etherification involving a primary halide was also examined. The monomers thus obtained were successfully polymerised by a free radical mechanism, yielding unbranched linear and soluble polymers with pending sucrose moieties, and some of their physical properties were determined.

Recent progress in the field of glycoconjugates

The ubiquity of glycoconjugates in nature and their role in different biological processes, has led to the development of several methodologies to synthesize these molecules. Synthetic glycoconjugates are now used to answer a variety of glycoconjugate-related biological questions and have provided new potential vaccines against cancer, viral, and bacterial infections and new biotechnological tools. This review aims to collect and compile the recent advances in the field of glycopeptides, glycoproteins, and glycolipid synthesis and also to update the previous reviews made on this subject. Finally, by highlighting the successes and failures of past research, we hope that this review will inspire fruitful research in this important medicinal chemistry field.

Synthesis of Hydrophilic and Amphiphilic Acryl Sucrose Monomers and Their Copolymerisation with Styrene, Methylmethacrylate and α- and β-Pinenes

Herein, we report the synthesis of monomethacryloyl sucrose esters, and their successful free radical homo- and co-polymerisation with styrene, methylmethacrylate, α-and β-pinene. The chemical, physical, structural and surface chemical properties of these polymers, containing a hydrophobic olefin backbone and hydrophilic sugar moieties as side chains, have been investigated. Biodegradation tests of the copolymer samples by a microbial fungal culture (Aspergillus niger) method showed good biodegradability. The chemical structure and surface chemistry of the synthesized homo- and co-polymers demonstrate their potential technological relevance as amphiphilic and biodegradable polymers.

Reaction Between Oxophosphorus Acids and Glycine

Abstract 2-Hydroxyesters of oxophosphorus acids (hypophosphorous, phosphorous and phosphoric) react with glycine to give amidoglycine-H-phosphinate, cyclic phospho-amidoanhydrideglycine-H-phosphonate and cyclic phosphoamidoanhydrideglycinephosphate. The reaction proceeds easily and in high yields under mild conditions because of the effect of vicinally hydroxy group as intramolecular catalyst on the reactivity of the ester bonds.

Determination of the rate of cure of epoxy resin/maleic anhydride/Lewis acids

Abstract The rates of cure of bisphenol A based epoxy resin and its mixtures with diethylene glycole based epoxy resin with maleic anhydride and accelerator BF 3 etherate were measured from dependences of degree of cure with time. The degree of cure was calculated using the following methods: amount of gel fraction, calorimetry and IR spectroscopy. The activity of the accelerator BF 3 etherate was compared with three Lewis acids: AlCl 3 , TiCl 4 and TlCl 3 . The activity of accelerators was evaluated by the rate of cure and was compared with their molecular characteristics, calculated from molecular structure of the compounds.

Sucrose chemistry: Fast and Efficient Microwave-assisted Protocols for the Generation of Sucrose-Containing Monomer Libraries

Sucrose is a carbohydrate feedstock of low molecular weight which is ubiquitous in its availability and is of relatively low cost (Lichtenthaler and Mondel, 1997). The potential value of sucrose as a raw material has been recognized for many years and has been the subject of considerable research. The quest for novel, sustainable, but also structurally robust materials is gaining momentum as the pressure on our environment is building up and the progressive changeover of the chemical industry to renewable feedstock for their raw materials emerges as an inevitable necessity. Although extensive work has been done on the synthesis of glycopolymers, more research efforts are needed to bridge the conceptual, technological and economical gap between fossil hydrocarbons and renewable carbohydrates (Khan, 1984). Sucrose is a particularly appropriate material for use in the formation of many products of commercial significance produced currently from petroleum-based materials, because: it is a naturally occurring, relatively abundant renewable resource; it is polyfunctional, with three reactive primary hydroxyl groups that can be readily and selectively derivatized; it is a 1-2’ linked disaccharide and therefore a nonreducing sugar and thus it does not have the potential for the wide variety of reactions that reducing sugars have; it is a naturally occurring carbohydrate, therefore products based on it are potentially biocompatible and biodegradable (Davis and Fairbanks, 2002). As part of a program directed toward the valorization of sucrose by incorporating it into polymers, its conversion to natural compounds, and its possible application as a chiral auxiliary in selective asymmetric cycloaddition (Lichtenthaler and Peters, 2004), we needed to obtain derivatives of sucrose which could be functionalized easily and selectively at the primary hydroxyl groups (Fig. 1) (Jarosz and Mach, 2002). For this, the development of short and easy routes for the preparation of larger quantities of these target molecules was necessary.

Films Based on New Methacrylate Monomers: Synthesis, Characterisation and Electro-Optical Properties

A number of liquid crystal monomers based on methacrylate derivatives were synthesised by novel mild and solventless procedures under microwave irradiation. Their photo- and thermo assisted homo- and co-polymerizations with glycidyl methacrylate were investigated. The resulting polymers were characterised by NMR, GPC, DSC, and SEM to determine their structures and properties. The effects of the structures of the monomers on the electro-optical properties were correlated.

Determination of the activity of phosphorus containing compounds on the crosslinking of epoxy resins by acid anhydrides

Abstract The crosslinking of epoxy resin by acid anhydrides was accelerated by several phosphorus containing compounds. The activity of the accelerators was evaluated by the rate of cure W and with activation energy E act . Some of the accelerators were obtained by a new method and were new compounds. The activity of the accelerators was compared with their p K a values. The accelerators decreased the time and the temperature of crosslinking and the effect of chemical structure of acid anhydrides.

Fast synthesis employing a microwave assisted neat protocol of new monomers potentially useful for the preparation of PDLC films

AbstractIt has been reported that the length of the molecular chain and the rigidity of molecules influence the structure of the polymer network in PDLC films and hence the electro-optical properties of the composites. Herein, a series of new aromatic monomeric monomethacrylates, bismethacrylates and monovinylbenzene derivatives with a mesogenic core were successfully synthesized under microwave irradiation. The microwave assisted synthesis resulted in decreased reaction times, reduced solvent requirement, increased operational simplicity, and in most cases, improved yields and selectivity.