Multivalent ligand mimetics of LecA from P. aeruginosa: synthesis and NMR studies.

Molecular recognition of glycans plays an important role in glycomic and glycobiology studies. For example, pathogens have a number of different types of lectin for targeting host sugars. In bacteria, lectins exist sometimes as domains of bacterial toxins and exploit adhesion to glycoconjugates as a means of entering host cells. Herein, we describe the synthesis of three glycodendrons with the aim to dissect the fine structural details involved in the multivalent carbohydrate-protein interactions. LecA, from the pathogen Pseudomonas aeruginosa, has been used to characterize galactose dendrons interaction using one of the most widespread NMR technique for the elucidation of receptor-ligand binding in solution, the saturation transfer difference (STD) NMR. Furthermore, the effective hydrodynamic radius of each dendrimer recognized by LecA was estimated from the diffusion coefficients determined by pulsed-field-gradient stimulated echo (PFG-STE) NMR experiments.

New synthesis and biological evaluation of uniflorine A derivatives: towards specific insect trehalase inhibitors.

7-Deoxy-uniflorine A (6), synthesized ex novo with a straightforward and simple strategy, and the analogues 4, 5 and 7, were evaluated as potential inhibitors of insect trehalase from Chironomus riparius and Spodoptera littoralis. All the compounds were tested against porcine trehalase as the mammalian counterpart and α-amylase from human saliva as a relevant glucolytic enzyme. The aim of this work is the identification of the simplest pyrrolizidine structure necessary to impart selective insect trehalase inhibition, in order to identify new specific inhibitors that can be easily synthesized compared to our previous reports with the potential to act as non-toxic insecticides and/or fungicides. All the derivatives 4­7 proved to be active (from low micromolar to high nanomolar range activity) towards insect trehalases, while no activity was observed against α-amylase. In particular, the natural compound uniflorine A and its 7-deoxy analogue were found to selectively inhibit insect trehalases, as they are inactive towards the mammalian enzyme. The effect of compound 6 was also analyzed in preliminary in vivo experiments. These new findings allow the identification of natural uniflorine A and its 7-deoxy analogue as the most promising inhibitors among a series of pyrrolizidine derivatives for future development in the agrochemical field, and the investigation also outlined the importance of the stereochemistry at C-6 of pyrrolizidine nucleus to confer such enzyme specificity.

Bifunctional dendrons for multiple carbohydrate presentation via carbonyl chemistry.

The synthesis of new dendrons of the generations 0, 1 and 2 with a double bond at the focal point and a carbonyl group at the termini has been carried out. The carbonyl group has been exploited for the multivalent conjugation to a sample saccharide by reductive amination and alkoxyamine conjugation.

N-Bridged 1-deoxynojirimycin dimers as selective insect trehalase inhibitors.

A small set of N-bridged 1-deoxynojirimycin dimers has been synthesized and evaluated as potential inhibitors of insect trehalase from midge larvae of Chironomus riparius, porcine trehalase as the mammalian counterpart and α-amylase from human saliva. All the tested compounds (2-4) proved to be active (micromolar range activity) against insect trehalase, showing selectivity toward the insect glycosidase. No activity was observed against α-amylase.

Dendron synthesis and carbohydrate immobilization on a biomaterial surface by a double-click reaction.

The synthesis of new dendrons and their immobilization on collagen patches via thiol-ene photoclick reaction, followed by chemoselective alkoxyamino-carbonyl conjugation to carbohydrates is presented. XPS, FTIR, and ELLA assays confirmed the effectiveness of the collagen multivalent neoglycosylation.

Recent approaches to novel antibacterials designed after LPS structure and biochemistry.

Lipopolysaccharides (LPSs), which constitute the lipid portion of the outer leaflet of Gram-negative bacteria, are essential for growth, and are responsible for a variety of biological effects associated with Gram-negative sepsis. LPSs are amphiphilic molecules comprising three regions: lipid A, the core region, and a polysaccharide portion; the lipid A was proven to represent the toxic principle of endotoxic active lipopolysaccharides. In addition, it is known that the minimal conserved structure of LPS is the lipophylic oligoasaccharidic structure containing Kdo residues linked to the-LipA moiety. Thus, the design and development of novel antibacterial drugs can focus on different aspects, related to the biosynthesis and chemical features of LPS: 1) Inhibitors of lipid A biosynthesis 2) Inhibitors of Kdo biosynthesis. Both Kdo and Lipid A are needed for the construction of the minimum structural element Kdo2-LipidA, needed for bacterial survival. Any inhibitors acting on the biogenetic pathway of this molecule can act as antibacterial. 3) Antagonists of the interaction between endotoxins and the host receptors: LPS is recognised by the CD14 and the Toll-like receptor (TLR)-4/MD2 complex, where Lipid A is the crucial moiety in the interaction. Any drug acting as an antagonist of this process can have antisepsis potential. Considerable efforts have been made in this direction to identify natural or synthetic molecules able to interfere with the interaction between LPS and inflammatory cells. This review will highlight recent efforts in the design and biological activity of enzyme inhibitors and antagonist acting on the 3 key aspects outlined above.

Synthesis and characterization of a paramagnetic sialic acid conjugate as probe for magnetic resonance applications.

Magnetic Resonance Imaging (MRI) using paramagnetic systems as contrast agents is receiving increased attention as diagnostic tool in the clinic. At the same time, NMR of paramagnetic systems can also be applied in biochemical fields; for example, the use of Paramagnetic Relaxation Enhancement (PRE) allows structure refinement and the analysis of transient dynamic processes involved in macromolecular complex formation. Herein we report the synthesis and computational characterization of a new DOTA-like sialic acid conjugate, which can be used both in MRI and PRE applications when coordinated to a suitable paramagnetic metal.

Synthesis and biological evaluation of nojirimycin- and pyrrolidine-based trehalase inhibitors.

A small set of nojirimycin- and pyrrolidine-based iminosugar derivatives has been synthesized and evaluated as potential inhibitors of porcine and insect trehalases. Compounds 12, 13 and 20 proved to be active against both insect and porcine trehalases with selectivity towards the insect glycosidase, while compounds 10, 14 and 16 behaved as inhibitors only of insect trehalase. Despite the fact that the activity was found in the micromolar range, these findings may help in elucidating the structural features of this class of enzymes of different origin, which are still scarcely characterised.

Discovery and design of carbohydrate-based therapeutics.

IMPORTANCE OF THE FIELD: Till now, the importance of carbohydrates has been underscored, if compared with the two other major classes of biopolymers such as oligonucleotides and proteins. Recent advances in glycobiology and glycochemistry have imparted a strong interest in the study of this enormous family of biomolecules. Carbohydrates have been shown to be implicated in recognition processes, such as cell-cell adhesion, cell-extracellular matrix adhesion and cell-intruder recognition phenomena. In addition, carbohydrates are recognized as differentiation markers and as antigenic determinants. Due to their relevant biological role, carbohydrates are promising candidates for drug design and disease treatment. However, the growing number of human disorders known as congenital disorders of glycosylation that are being identified as resulting from abnormalities in glycan structures and protein glycosylation strongly indicates that a fast development of glycobiology, glycochemistry and glycomedicine is highly desirable. AREAS COVERED IN THIS REVIEW: The topics give an overview of different approaches that have been used to date for the design of carbohydrate-based therapeutics; this includes the use of native synthetic carbohydrates, the use of carbohydrate mimics designed on the basis of their native counterpart, the use of carbohydrates as scaffolds and finally the design of glyco-fused therapeutics, one of the most recent approaches. The review covers mainly literature that has appeared since 2000, except for a few papers cited for historical reasons. WHAT THE READER WILL GAIN: The reader will gain an overview of the current strategies applied to the design of carbohydrate-based therapeutics; in particular, the advantages/disadvantages of different approaches are highlighted. The topic is presented in a general, basic manner and will hopefully be a useful resource for all readers who are not familiar with it. In addition, in order to stress the potentialities of carbohydrates, several examples of carbohydrate-based marketed therapeutics are given. TAKE HOME MESSAGE: Carbohydrates are a rich class of natural compounds, possessing an intriguing and still not fully understood biological role. This richness offers several strategies for the design of carbohydrate-based therapeutics.

Pyrrolo[2,1-c][1,4]benzodiazepine as a scaffold for the design and synthesis of anti-tumour drugs.

Compounds that bind in the minor groove of DNA have found use in the experimental treatment of cancer and certain infectious diseases. Furthermore, agents which target and can recognize discrete sequences of DNA have the potential to offer selective therapies by modulating the activity of specific transcription factors or genes. For this reason, a number of sequence-selective DNA binding agents have been evaluated with a range of affinities and recognition fidelities. In this respect, the pyrrolo[2,1-c][1,4]benzodiazepines (PBDs) are of interest as they bind to guanine residues in the minor groove with a preference for Pu-G-Pu sequences. A dramatic increase in cytotoxicity and sequence selectivity has been achieved by linking two PBD units to form PBD dimers as cross-linking agents on opposite DNA strands (e.g., interstrand cross-links). SJG-136 is currently undergoing Phase I evaluation in both the United States (through the NCI) and United Kingdom (through Cancer Research United Kingdom). This review will focus on design, synthesis and structure activity relationship studies of pyrrolobenzodiazepines as anticancer therapeutics reported since 2003.