Yves Queneau

Recent progress in the synthesis of carbohydrate-based amphiphilic materials: the examples of sucrose and isomaltulose

In the context of the use of carbohydrates obtained from agricultural crops, the search for amphiphilic derivatives is one of the most developed aspects. Indeed, due to the high polarity and the functional richness of sugars, many different structures can be targeted, with a wide range of physicochemical properties, either for large scale products of industrial interest, or for fine applications at the chemistry-biology interface. Among carbohydrates arising from agricultural resources, sucrose is especially interesting because of its very large production scale in the world (ca. 160Mt/year, ca. 20Mt/year of which in the European Community). Here, we describe the research accomplished in our group dealing with the synthesis and the study of the properties of amphiphilic derivatives prepared from sucrose as well as from another very available disaccharide, isomaltulose.

Transesterification of Sucrose in Organic Medium: Study of Acyl Group Migrations

The tendency of the acyl groups located on the glucose part of sucrose fatty acid esters to undergo intramolecular migrations in organic medium and the regioselectivity of some transesterifications of sucrose were investigated by HPLC, in situ NMR spectroscopy and preparative methods. Extensive acylation on secondary positions of the glucose moiety followed by migrations is general for base catalysed transesterification. The stability of 3‐ and 6‐O‐acyl derivatives, two isomers being thermodynamically favored compared to others, was studied in a series of conditions. It is shown that the presence of water catalyzes the migration of the ester at OH‐3 towards OH‐6 in organic basic medium, whereas the ester at OH‐6 appears more stable under either acidic or basic conditions. †This paper is dedicated to Professor Gérard Descotes on the occasion of his 70th birthday, in acknowledgement of his accomplishments in the field of carbohydrate chemistry, and of his continuing efforts for developing the use of renewable sugars for chemistry.

Synthesis and Thermotropic Behavior of Simple New Glucolipid Amides

The coupling reaction of 3,4,6‐tri‐O‐acetyl‐α‐d‐glucopyranoside 2‐O‐lactone 1 (α‐CMGL) with two kinds of lipophilic amines, aminosteroids and fatty amines, efficiently yielded, after deprotection, the corresponding free α‐glucolipid amides. The latter family of compounds exhibited good thermal stability, allowing the higher homologs having longer linear fatty chains or saturated steroids to possess lamellar smectic A phases.

Oxidation of two major disaccharides: sucrose and isomaltulose

The chemical oxidation of sucrose, isomaltulose and methyl isomaltuloside is described, with special focus on the use of the NaOCl–TEMPO oxidizing system.

N,N’-alkylated Imidazolium-Derivatives Act as Quorum-Sensing Inhibitors Targeting the Pectobacterium atrosepticum-Induced Symptoms on Potato Tubers

Bacteria belonging to the Pectobacterium genus are the causative agents of the blackleg and soft-rot diseases that affect potato plants and tubers worldwide. In Pectobacterium, the expression of the virulence genes is controlled by quorum-sensing (QS) and N-acylhomoserine lactones (AHLs). In this work, we screened a chemical library of QS-inhibitors (QSIs) and AHL-analogs to find novel QSIs targeting the virulence of Pectobacterium. Four N,N′-bisalkylated imidazolium salts were identified as QSIs; they were active at the μM range. In potato tuber assays, two of them were able to decrease the severity of the symptoms provoked by P. atrosepticum. This work extends the range of the QSIs acting on the Pectobacterium-induced soft-rot disease.

A continuous spectrophotometric assay that distinguishes between phospholipase A1 and A2 activities

A new spectrophotometric assay was developed to measure, continuously and specifically, phospholipase A1 (PLA1) or phospholipase A2 (PLA2) activities using synthetic glycerophosphatidylcholines (PCs) containing α-eleostearic acid, either at the sn-1 position [1-α-eleostearoyl-2-octadecyl-rac-glycero-3-phosphocholine (EOPC)] or at the sn-2 position [1-octadecyl-2-α-eleostearoyl-rac-glycero-3-phosphocholine (OEPC)]. The substrates were coated onto the wells of microtiter plates. A nonhydrolyzable ether bond, with a non-UV-absorbing alkyl chain, was introduced at the other sn position to prevent acyl chain migration during lipolysis. Upon enzyme action, α-eleostearic acid is liberated and then solubilized into the micellar phase. The PLA1 or PLA2 activity was measured by the increase in absorbance at 272 nm due to the transition of α-eleostearic acid from the adsorbed to the soluble state. EOPC and OEPC differentiate, with excellent accuracy, between PLA1 and PLA2 activity. Lecitase®, guinea pig pancreatic lipase-related protein 2 (known to be a PLA1 enzyme), bee venom PLA2, and porcine pancreatic PLA2 were all used to validate the assay. Compared with current assays used for continuously measuring PLA1 or PLA2 activities and/or their inhibitors, the development of this sensitive enzymatic method, using coated PC substrate analogs to natural lipids and based on the UV spectroscopic properties of α-eleostearic acid, is a significant improvement.

Chapter 15:Liquid crystal glycolipids

There is a growing consciousness that the observed liquid crystallinity of many biological materials be related with their biological functions. While the survival of living systems depends on the flexibility and reformability of structures, the combination of softness and structure of the liquid crystalline state seems to determine the functionality of biological materials. The richest sources of liquid crystals derived from living systems are found in cell membranes, and glycolipids, which are important components of cell membranes, show fascinating self-assembling behaviour. In this chapter, by examining typical examples of liquid crystalline glycolipids with respect to their chemical structure, we will illustrate our understanding of the self-assembling and self-organising properties of glycolipids to the point of predictivity for rational design of mesomorphism in such systems.

Carbohydrate steroid hybrid architectures: the viewpoint of amphiphilicity and self-organisation

Carbohydrate steroid hybrids (steroid glycosides, glycosyl steroids and related compounds) are ubiquitous natural products, with immense structural diversity. They also show a common feature of being amphiphilic in character, which will be the major subject reviewed in this chapter. It will be preceded by an introduction on the occurrence and properties of glycosteroids, and their classification into three main sub-families based on their overall molecular shape and polarity where systems have: (i) one saccharidic part and one steroidal part, possibly including a spacer chain; (ii) saccharidic connections at two different points of the steroid, and (iii) an additional appendage that can be either polar or non-polar.

A Continuous and Sensitive Spectrophotometric Assay for Lipase and Phospholipase A Activities Using α-Eleostearic Acid-Containing Substrates

To date, several sensitive methods, based on radiolabeled elements or sterically hindered fluorochrome groups, are usually employed to screen lipase and phospholipase A (PLA) activities. Here, a new ultraviolet spectrophotometric assay for lipase or PLA was developed using natural triglycerides or synthetic glycerophosphatidylcholines containing α-eleostearic acid (9Z, 11E, 13E-octadecatrienoic acid) purified from Aleurites fordii seed oil. The conjugated triene present in α-eleostearic acid constitutes an intrinsic chromophore and consequently confers strong UV absorption properties of this free fatty acid as well as of lipid substrates harboring it. The substrate was coated into the wells of a microplate, and the lipolytic activities were measured by the absorbance increase at 272xa0nm due to the transition of α-eleostearic acid moiety from the adsorbed to the soluble state. This continuous assay is compatible with a high-throughput screening method and can be applied specifically to the screening of new potential lipase, PLA1 and PLA2 inhibitors.