Antony E. Fernandes

Sequence-Specific Peptide Synthesis by an Artificial Small-Molecule Machine

Ribosomal Rotaxane? The ribosome is an extraordinarily sophisticated molecular machine, assembling amino acids into proteins based on the precise sequence dictated by messenger RNA. Lewandowski et al. (p. 189) have now taken a step toward the preparation of a stripped-down synthetic ribosome analog. Their machine comprises a rotaxane—a ring threaded on a rod—in which the ring bears a pendant thiol that can pluck amino acids off the rod; the terminal nitrogen then wraps around to form a peptide bond and liberate the thiol for further reaction. The system was able to link three amino acids in order from the preassembled rod. A macrocycle threaded on a rod can catalytically insert several amino acids placed along its path into a peptide chain. The ribosome builds proteins by joining together amino acids in an order determined by messenger RNA. Here, we report on the design, synthesis, and operation of an artificial small-molecule machine that travels along a molecular strand, picking up amino acids that block its path, to synthesize a peptide in a sequence-specific manner. The chemical structure is based on a rotaxane, a molecular ring threaded onto a molecular axle. The ring carries a thiolate group that iteratively removes amino acids in order from the strand and transfers them to a peptide-elongation site through native chemical ligation. The synthesis is demonstrated with ~1018 molecular machines acting in parallel; this process generates milligram quantities of a peptide with a single sequence confirmed by tandem mass spectrometry.

Rotaxane-based propeptides: protection and enzymatic release of a bioactive pentapeptide.

Ring of protection: A [2]rotaxane 1 protects and selectively releases a bioactive pentapeptide. The rotaxane macrocycle provides a defensive shield that very significantly improves the poor stability of the peptide to both individual peptidases and the cocktail of enzymes present in human plasma. Glycosidase-catalyzed cleavage of a carbohydrate ‘stopper’ in the rotaxane triggers release of the parent peptide

Design of Self-Immolative Linkers for Tumour-Activated Prodrug Therapy

The main drawback of most cancer chemotherapy is its relatively low ability to target tumour cells versus normal cells. As a consequence, chemotherapy is usually connected with severe side effects due to the toxicity of traditional cytostatic agents towards normal tissues. A few years ago, the site-specific activation of non-toxic prodrugs in tumours has been proposed in order to enhance the selectivity for the killing of cancer cells. Within this framework, most of the prodrugs that have been designed were three part compounds comprising trigger, linker and effector units. The main function of the linker is to release the effector unit after selective trigger activation via a spontaneous chemical breakdown. However, its structure also affects significantly many prodrug properties such as stability, pharmacokinetic, organ distribution, bioavailability or trigger activation. This review, focussed on the linker unit, is an update of our previous article published in 2002. It deals with recent advances in the design of prodrug linkers including new delivery systems such as elongated linkers or self-immolative dendrimers.

Correlation between the Structure and Wettability of Photoswitchable Hydrophilic Azobenzene Monolayers on Silicon

Photoresponsive monolayers of hydrophilically substituted azobenzenes have been prepared by reaction on aminosilane monolayers on silicon surfaces. Grafting densities in the 0.2-1.0 molecule/nm(2) range were determined by X-ray reflectometry. The monolayers exhibit reversible photoisomerization, switching from a more hydrophilic trans state to a less hydrophilic cis state upon UV irradiation, in contrast with the usual behavior of most azobenzene monolayers that switch from a less to a more hydrophilic state. This indicates that the wettability is not dominated by the change in the dipole moment of the azobenzene moiety but originates from variations in the composition of the outer surface of the monolayers resulting from the reorientation of the substituent groups. The light-driven change in the water contact angle correlates linearly with the grafting density but remains small. However, the wettability contrast can be increased by forcing the molecules to stand in an improved vertical orientation, either by densifying the underlying aminosilane monolayer or by filling the voids left at the bottom of the layer of grafted azobenzene molecules.

Synthesis and pharmacological evaluation of carboxycoumarins as a new antitumor treatment targeting lactate transport in cancer cells.

Under hypoxia, cancer cells consume glucose and release lactate at a high rate. Lactate was recently documented to be recaptured by oxygenated cancer cells to fuel the TCA cycle and thereby to support tumor growth. Monocarboxylate transporters (MCT) are the main lactate carriers and therefore represent potential therapeutic targets to limit cancer progression. In this study, we have developed and implemented a stepwise in vitro screening procedure on human cancer cells to identify new potent MCT inhibitors. Various 7-substituted carboxycoumarins and quinolinone derivatives were synthesized and pharmacologically evaluated. Most active compounds were obtained using a palladium-catalyzed Buchwald-Hartwig type coupling reaction, which proved to be a quick and efficient method to obtain aminocarboxycoumarin derivatives. Inhibition of lactate flux revealed that the most active compound 19 (IC50 11 nM) was three log orders more active than the CHC reference compound. Comparison with warfarin, a conventional anticoagulant coumarin, further showed that compound 19 did not influence the prothrombin time which, together with a good in vitro ADME profile, supports the potential of this new family of compounds to act as anticancer drugs through inhibition of lactate flux.

Molecular Engineering of Trifunctional Supported Catalysts for the Aerobic Oxidation of Alcohols

We describe a simple and general method for the preparation and molecular engineering of supported trifunctional catalysts and their application in the representative Cu/TEMPO/NMI-catalyzed aerobic oxidation of benzyl alcohol. The methodology allows in one single step to immobilize, with precise control of surface composition, both pyta, Cu(I) , TEMPO, and NMI sites on azide-functionalized silica particles. To optimize the performance of the heterogeneous trifunctional catalysts, synergistic interactions are finely engineered through modulating the degree of freedom of the imidazole site as well as tuning the relative surface composition, leading to catalysts with an activity significantly superior to the corresponding homogeneous catalytic system.

Thicker is Better? Synthesis and Evaluation of Well-Defined Polymer Brushes with Controllable Catalytic Loadings

Polymer brushes (PBs) have been used as supports for the immobilization of palladium complexes on silicon surfaces. The polymers were grown by surface-initiated atom-transfer radical polymerization (SI-ATRP) and postdecorated with dipyridylamine (dpa) ligands. The pendant dpa units were in turn complexed with [Pd(OAc)(2)] to afford hybrid catalytic surfaces. A series of catalytic samples of various thicknesses (ca. 20-160 nm) and associated palladium loadings (ca. 10-45 nmol  cm(-2)) were obtained by adjusting the SI-ATRP reaction time and characterized by ellipsometry, X-ray reflectivity, X-ray photoelectron spectroscopy, and inductively coupled plasma mass spectrometry (ICP-MS). ICP-MS revealed a near-linear relationship between thickness of the polymer brush and palladium content, which confirmed the robustness of the preparation and postmodification sequence presented herein, rendering possible the creation of functional architectures with predefined catalytic potential. The activities of the catalytic PBs were determined by systematically exploring a full range of substrate-to-catalyst ratios in a model palladium(0)-catalyzed reaction. Quantitative transformations were observed for loadings down to 0.03 mol % and a maximum turnover number (TON) of around 3500 was established for the system. Comparison of the catalytic performances evidenced a singular influence of the thickness on conversions and TONs. The limited recyclability of the hairy catalysts has been attributed to palladium leaching.

One “Click” to controlled bifunctional supported catalysts for the Cu/TEMPO-catalyzed aerobic oxidation of alcohols

A simple and reliable methodology is described for the preparation of heterogeneous bifunctional catalysts with a high control over surface composition. The strategy relies on the grafting of a mix of catalytic components from an azide-functionalized silica platform using the CuAAC reaction. The resulting finely engineered supported catalysts are employed in the model Cu/TEMPO-catalyzed aerobic oxidation of benzylic alcohol.

Increased Catalytic Activity of Surface‐Immobilized Palladium Complexes in the Fluorogenic Deprotection of an Alloc‐Derivatized Coumarin

Catalytic surfaces have been prepared by complexation of palladium on self-assembled terpyridine monolayers on silicon. A reaction-based fluorogenic probe was developed to allow facile visualization of the catalytic potential of the surface. Superior activity of the immobilized catalyst compared with the homogeneous control reactions is demonstrated.

Grafting control of mainstay terpyridine self-assembled monolayers for the preparation of planar silicon surfaces with variable catalytic loadings.

Monolayers of terpyridine-derivatized silanes were self-assembled, with accurately controlled grafting densities, on single-crystal silicon surfaces. Complexation of the resulting terpyridine monolayers with Pd(OAc)(2) afforded a series of catalytic surfaces covering a full range of Pd loadings (0.14-0.85 nmol.cm(-2)) in the aim to explore their impact on catalysis methodically. X-ray reflectivity (XRR), X-ray photoelectron spectroscopy (XPS), and inductively coupled plasma mass spectrometry (ICP-MS) were combined to afford a precise picture of the grafting density, chemical composition, and catalyst loadings of the surfaces investigated here. We report that the control of the terpyridine density and thus the control of catalytic loadings can be achieved through a fine modification of silanization concentrations, which affords surfaces with tunable catalytic activity.