Ricardo Riguera

Reliable and Efficient Procedures for the Conjugation of Biomolecules through Huisgen Azide–Alkyne Cycloadditions

The Cu(I)-catalyzed azide-alkyne cycloaddition (CuAAC) has been established as a powerful coupling technology for the conjugation of proteins, nucleic acids, and polysaccharides. Nevertheless, several shortcomings related to the presence of Cu, mainly oxidative degradation by reactive oxygen species and sample contamination by Cu, have been pointed out. This Minireview discusses key aspects found in the development of the efficient and benign functionalization of biomacromolecules through CuAAC, as well as the Cu-free strain-promoted azide-alkyne cycloaddition (SPAAC).

A practical guide for the assignment of the absolute configuration of alcohols, amines and carboxylic acids by NMR

A practical guide for the assignment of the absolute configuration of alcohols, amines and carboxylic acids by NMR is presented. The guide includes information required for the judicious selection of the most suitable auxiliary reagent (MPA, MTPA, BPG, 9-AMA and 9-AHA), derivatization procedures and NMR conditions (solvent and temperature) for each substrate, as well as a critical account on the reliability, scope and limitations of these applications.

Surpassing the Use of Copper in the Click Functionalization of Polymeric Nanostructures : A Strain-Promoted Approach

The limitations (depolymerization and Cu contamination) in the use of Cu(I)-catalyzed azide-alkyne [3 + 2] cycloadditions (CuAAC) for the selective click functionalization of polysaccharide-based systems have been efficiently surpassed using a strain-promoted approach (SPAAC). The SPAAC decoration of chitosan-g-poly(ethylene glycol) nanostructures with an immunoglobulin G under physiological conditions represents a step forward in the preparation of immunonanoparticles.

Click Chemistry for Drug Delivery Nanosystems

ABSTRACTThe purpose of this Expert Review is to discuss the impact of click chemistry in nanosized drug delivery systems. Since the introduction of the click concept by Sharpless and coworkers in 2001, numerous examples of click reactions have been reported for the preparation and functionalization of polymeric micelles and nanoparticles, liposomes and polymersomes, capsules, microspheres, metal and silica nanoparticles, carbon nanotubes and fullerenes, or bionanoparticles. Among these click processes, Cu(I)-catalyzed azide-alkyne cycloaddition (CuAAC) has attracted most attention based on its high orthogonality, reliability, and experimental simplicity for non-specialists. A renewed interest in the use of efficient classical transformations has been also observed (e.g., thiol-ene coupling, Michael addition, Diels-Alder). Special emphasis is also devoted to critically discuss the click concept, as well as practical aspects of application of CuAAC to ensure efficient and harmless bioconjugation.

A Nanomedicine Transports a Peptide Caspase-3 Inhibitor across the Blood–Brain Barrier and Provides Neuroprotection

Caspases play an important role as mediators of cell death in acute and chronic neurological disorders. Although peptide inhibitors of caspases provide neuroprotection, they have to be administered intracerebroventricularly because they cannot cross the blood–brain barrier (BBB). Herein, we present a nanocarrier system that can transfer chitosan nanospheres loaded with N-benzyloxycarbonyl-Asp(OMe)-Glu(OMe)-Val-Asp(OMe)-fluoromethyl ketone (Z-DEVD-FMK), a relatively specific caspase-3 inhibitor, across BBB. Caspase-3 was chosen as a pharmacological target because of its central role in cell death. Polyethylene glycol-coated nanospheres were conjugated to an anti-mouse transferrin receptor monoclonal antibody (TfRMAb) that selectively recognizes the TfR type 1 on the cerebral vasculature. We demonstrate with intravital microscopy that this nanomedicine is rapidly transported across the BBB without being measurably taken up by liver and spleen. Pre- or post-treatment (2 h) with intravenously injected Z-DEVD-FMK-loaded nanospheres dose dependently decreased the infarct volume, neurological deficit, and ischemia-induced caspase-3 activity in mice subjected to 2 h of MCA occlusion and 24 h of reperfusion, suggesting that they released an amount of peptide sufficient to inhibit caspase activity. Similarly, nanospheres inhibited physiological caspase-3 activity during development in the neonatal mouse cerebellum on postnatal day 17 after closure of the BBB. Neither nanospheres functionalized with TfRMAb but not loaded with Z-DEVD-FMK nor nanospheres lacking TfRMAb but loaded with Z-DEVD-FMK had any effect on either paradigm, suggesting that inhibition of caspase activity and subsequent neuroprotection were due to efficient penetration of the peptide into brain. Thus, chitosan nanospheres open new and exciting opportunities for brain delivery of biologically active peptides that are useful for the treatment of CNS disorders.

Probing the relevance of lectin clustering for the reliable evaluation of multivalent carbohydrate recognition.

Experiments by Surface Plasmon Resonance (SPR) illustrate the relevance of lectin density for the reliable evaluation of binding efficiencies in surface-based multivalent carbohydrate recognition. The difference between affinity data obtained by solution and surface-based experiments is also stressed.

Synthesis and antihistaminic activity of 2-guanadino-3-cyanopyridines and pyrido[2,3-d]-pyrimidines

2-Guanadino-3-cyanopyridines 8-33 and pyrido[2,3-d]-pyrimidines 35-52 were synthesized by nucleophilic displacement and cyclization of the chloroamidines 6a-d easily obtained by reaction of 2-aminocyanopyridines 5a-d with phosgene iminium chloride and their action on the release of histamine by mast cells examined under immunological and chemical stimulus, with and without pre-incubation. Several 2-guanadino-3-cyanopyridines and pyrido[2,3-d]-pyrimidines are shown to be inhibitors of the release of histamine when stimulated with ovoalbumin as antigen or with polymer 48/80 as chemical stimulus. Guanadino-3-cyanopyridine 30 and pyrido[2,3-d]-pyrimidine 49 are the more active of all, inhibiting the release of histamine in all the conditions tested (30-60% inhibition). Guanadinocyanopyridines 15, 17, and 19 are very potent stimulators of the release of histamine (150-300%) while pyrido[2,3-d]-pyrimidines are mostly inactive. Compounds 28 and 14 present moderate in vitro cytotoxic activity against P-388, A-549, HT-29, and MEL-28 cell lines.

Click Chemistry with Polymers, Dendrimers, and Hydrogels for Drug Delivery

During the last decades, great efforts have been devoted to design polymers for reducing the toxicity, increasing the absorption, and improving the release profile of drugs. Advantage has been also taken from the inherent multivalency of polymers and dendrimers for the incorporation of diverse functional molecules of interest in targeting and diagnosis. In addition, polymeric hydrogels with the ability to encapsulate drugs and cells have been developed for drug delivery and tissue engineering applications. In the long road to this successful story, pharmaceutical sciences have been accompanied by parallel advances in synthetic methodologies allowing the preparation of precise polymeric materials with enhanced properties. In this context, the introduction of the click concept by Sharpless and coworkers in 2001 focusing the attention on modularity and orthogonality has greatly benefited polymer synthesis, an area where reaction efficiency and product purity are significantly challenged. The purpose of this Expert Review is to discuss the impact of click chemistry in the preparation and functionalization of polymers, dendrimers, and hydrogels of interest in drug delivery.

The structures and stereochemistry of cytotoxic sesquiterpene quinones from dactylospongia elegans

Abstract The cytotoxicity of a crude extract from Dactylospongia elegans stimulated a search for the active constituents. The structures and absolute stereochemistry are elucidated for four new 9, 11,18, 19, and thirteen previously described compounds, 3, 4, 6a, 7, 8, 10, 12 - 17, 21. These compounds were isolated from collections of D. elegans obtained from three different Indo-Pacific regions, Fiji, Papua New Guinea, and Thailand. This species appears to elaborate a broader range of the mixed biogenesis sesquiterpene-hydroquinone (-quinone) metabolites in comparison to those of other sponges or seaweeds. Three compounds, 4, 9, and 13, were potent (IC50s were less than 1 μg/mL). The quinone ring appears to be essential for this in vitro activity.

Piperazine N-substituted naphthyridines, pyridothienopyrimidines and pyridothienotriazines: new antiprotozoals active against Philasterides dicentrarchi

New antiprotozoals active against Philasterides dicentrarchi, the causative agent of scuticociliatosis in farmed turbot and Black Sea bass-bream, have been synthesised and tested. The most active compounds posses a piperazine ring, generally N-bonded to the heterocycle, and are the 1,8-naphthyridines, 2f and 5o, the pyridothienopyrimidine (7), and the pyridothienotriazines, 8, 9, 12d, 12f, 12h, 12m and 12k. Pyridothienotriazine (12k) presents the same activity (Lethal Dose, LD=0.8/1.5 mg L(-1)) as the well-known antiparasitics niclosamide and oxyclozanide.