A mild Boc deprotection and the importance of a free carboxylate

We report a facile and rapid removal of Boc protecting groups using microwave heating in H₂O, with deprotection only requiring a free carboxylic acid group in the starting material. Unlike previous approaches, no additional reagents are required.     

Regioselectivity among six secondary hydroxyl groups: selective acylation of the least reactive hydroxyl groups of inositol

We report the first, general and selective acylation of the least reactive hydroxyl group among six secondary hydroxyl groups of inositol in high yield, using very cheap and easy-to-make H(2)SO(4)-silica as the catalyst, providing easy access to bioactive molecules.     

Paper-based device for rapid typing of secondary human blood groups

We report the use of bioactive paper for typing of secondary human blood groups. Our recent work on using bioactive paper for human blood typing has led to the discovery of a new method for identifying haemagglutination of red blood cells. The primary human blood groups, i.e., ABO and RhD groups, have been successfully typed with this method. Clinically, however, many secondary blood groups can also cause fatal blood transfusion accidents, despite the fact that the haemagglutination reactions of secondary blood groups are generally weaker than those of the primary blood groups. We describe the design of a user-friendly sensor for rapid typing of secondary blood groups using bioactive paper. We also present mechanistic insights into interactions between secondary blood group antibodies and red blood cells obtained using confocal microscopy. Haemagglutination patterns under different conditions are revealed for optimization of the assay conditions.     

One-Pot Sequential Kumada–Tamao–Corriu Couplings of (Hetero)Aryl Polyhalides in the Presence of Grignard-Sensitive Functional Groups Using Pd-PEPPSI-IPentCl

We report a general and rapid chemoselective Kumada–Tamao–Corriu (KTC) cross-coupling of aryl bromides in the presence of chlorides or triflates with functionalized Grignard reagents at 0 °C in 15 min by using Pd-PEPPSI-IPent^Cl ( C4 ). Nucleophiles and electrophiles (or both) can contain Grignard-sensitive functional groups (-CN, -COOR, etc.). Control experiments together with DFT calculations suggest that transmetallation is rate limiting for the selective cross-coupling of Br in the presence of Cl/OTf with functionalized Grignard reagents. One-pot sequential KTC/KTC cross-couplings with bromo–chloro arenes have been demonstrated for the first time. We also report the one-pot sequential KTC/Negishi cross-couplings using C4 showcasing the versatility of this methodology.     

Color test for the detection of resin-bound aldehyde in solid-phase combinatorial synthesis

We report the development of a sensitive and specific color test for the detection of the presence of resin-bound aldehyde groups using 4-amino-3-hydrazino-5-mercapto-1,2,4-triazole (Purpald). Aldehyde resin turns dark-brown to purple after a 5 min reaction followed by a 10 min air oxidation period. Resins that possess other functional groups (i.e., ketone, ester, amide, alcohol, and carboxylic acid) do not change color under the same conditions. The detection limit is 20 micromol/g for polystyrene-based aldehyde resins.     

Remote electronic effects in the rhodium-catalyzed nucleophilic ring opening of oxabenzonorbornadienes

We report the application of our rhodium-catalyzed nucleophilic ring-opening methodology to unsymmetrically arene-substituted oxabenzonorbornadienes. The regioselectivity of the ring opening was investigated using a variety of nucleophiles that led to a broad selection of dihydronaphthalene products. It was found that good to excellent regioselectivities are obtained using strongly pi-donating substituents, whereas sigma-donating and electron-withdrawing functionalities have a minimal effect. Post ring-opening manipulations of functional groups in the dihydronaphthalene products were shown to give efficient access to mono- and diamine tetrahydronaphthalene building blocks.     

A highly efficient, green, rapid, and chemoselective oxidation of sulfides using hydrogen peroxide and boric acid as the catalyst under solvent-free conditions

We report boric acid as a highly efficient and eco-friendly catalyst for the selective oxidation of sulfides to sulfoxides or sulfones, in excellent yields under solvent-free conditions, using 30% hydrogen peroxide as an oxidant. Various sulfides possessing functional groups such as alcohol, ester, and aldehyde are successfully and selectively oxidized without affecting sensitive functionalities.     

Electron transport through rectifying self-assembled monolayer diodes on silicon: Fermi-level pinning at the molecule-metal interface

We report the synthesis and characterization of molecular rectifying diodes on silicon using sequential grafting of self-assembled monolayers of alkyl chains bearing a pi group at their outer end (Si/sigma-pi/metal junctions). We investigate the structure-performance relationships of these molecular devices, and we examine the extent to which the nature of the pi end group (change in the energy position of their molecular orbitals) drives the properties of these molecular diodes. Self-assembled monolayers of alkyl chains (different chain lengths from 6 to 15 methylene groups) functionalized by phenyl, anthracene, pyrene, ethylene dioxythiophene, ethylene dioxyphenyl, thiophene, terthiophene, and quaterthiophene were synthesized and characterized by contact angle measurements, ellipsometry, Fourier transform infrared spectroscopy, and atomic force microscopy. We demonstrate that reasonably well-packed monolayers are obtained in all cases. Their electrical properties were assessed by dc current-voltage characteristics and high-frequency (1-MHz) capacitance measurements. For all of the pi groups investigated here, we observed rectification behavior. These results extend our preliminary work using phenyl and thiophene groups (Lenfant et al., Nano Lett. 2003, 3, 741). The experimental current-voltage curves were analyzed with a simple analytical model, from which we extracted the energy position of the molecular orbital of the pi group in resonance with the Fermi energy of the electrodes. We report experimental studies of the band lineup in these silicon/alkyl pi-conjugated molecule/metal junctions. We conclude that Fermi-level pinning at the pi group/metal interface is mainly responsible for the observed absence of a dependence of the rectification effect on the nature of the pi groups, even though the groups examined were selected to have significant variations in their electronic molecular orbitals.     

Convenient syntheses of bulky group containing imidazolium ionic liquids

We report syntheses of bulky group containing imidazolium based ionic liquids. The bulky groups were introduced at N‐1, C‐2, and N‐3 positions of the imidazole ring using convenient methodologies. J. Heterocyclic Chem., (2012).     

Side-by-side characterization of electron tunneling through monolayers of isomeric molecules: a combined experimental and theoretical study

We report a new experimental method for measuring relatively small differences in electron tunneling through two distinct monolayers. We place them side by side using scanning probe nanolithography and compare the tunneling currents by conductive probe atomic force microscopy under identical force, voltage, and tip contamination conditions. We demonstrate the validity of our approach by applying it to two isomeric molecules with similar length and functional groups, with only the position of two functional groups, one aromatic and the other aliphatic, being inverted with respect to each other. The relative values of the two tunneling currents, calculated using density functional theory and the Tersoff-Hamann approach, compare very well with the experimental data, providing us with an example of theory vs experiment agreement that is rather uncommon in this field.     

Stereospecific Conversion of Boronic Esters into Enones using Methoxyallene: Application in the Total Synthesis of 10-Deoxymethynolide

Enones are widely utilized linchpin functional groups in chemical synthesis and molecular biology. We herein report the direct conversion of boronic esters into enones using commercially available methoxyallene as a three-carbon building block. Following boronate complex formation by reaction of the boronic ester with lithiated-methoxyallene, protonation triggers a stereospecific 1,2-migration before oxidation generates the enone. The protocol shows broad substrate scope and complete enantiospecificity is observed with chiral migrating groups. In addition, various electrophiles could be used to induce 1,2-migration and give a much broader range of α-functionalized enones. Finally, the methodology was applied to a 14-step synthesis of the enone-containing polyketide 10-deoxymethynolide.     

Computation of the mean residence time of water in the hydration shells of biomolecules

An algorithm is presented within the context of the calculation of the time-relaxation behavior of the hydration shells around atomic sites in biomolecules. We report a calculation of the time-relaxation behavior of the first and second hydration shells of polar, hydrophobic, and charged groups in a protein, crambin. The water mean residence times around protein groups are obtained from averages over configurations sampled during a 325-ps molecular dynamics simulation of crambin in solution. A convolution arising in the calculation of the mean relaxation time is implemented using a parallel prefix operator. A new characterization is given of the parallel prefix operator as a linear transformation, and this formulation enables us to derive efficient factorization of the convolution as a product of two parallel prefix operations. The parallel prefix operations are implemented in logarithmic time. © John Wiley & Sons, Inc.     

Recognition properties of carboxylic acid bioisosteres: anion binding by tetrazoles, aryl sulfonamides, and acyl sulfonamides on a calix[4]arene scaffold

Tetrazoles and acyl sulfonamides are functional groups that are common in medicinal chemistry but virtually unexplored as recognition elements in supramolecular chemistry. We report here on the anion binding properties of these highly acidic N-H functional groups. We have prepared two new calixarene-based tetrazole-containing hosts, as well as new acetyl sulfonamide and benzoyl sulfonamide hosts. We also report on analogous hosts bearing the better-known aryl sulfonamide functional group as a point of comparison. We find that these hosts are competent anion binders and that the recognition of anions by these groups is highly dependent on their conformational preferences. We also report in detail on the preferred molecular shape of each acid bioisostere as determined by calculations and structural database surveys, and discuss how these shapes impact binding in the context of the reported hosts.     

Palladium-catalyzed aerobic oxidative cyclization of N-aryl imines: indole synthesis from anilines and ketones

We report here an operationally simple, palladium-catalyzed cyclization reaction of N-aryl imines, affording indoles via the oxidative linkage of two C-H bonds under mild conditions using molecular oxygen as the sole oxidant. The process allows quick and atom-economical assembly of indole rings from inexpensive and readily available anilines and ketones and tolerates a broad range of functional groups.     

Differential anodic oxidation of single organic linkage molecules enabling orthogonal bio-immobilization

We report a novel method for preparing electrode surfaces that present thiol-containing or thiol-reactive groups using a single organic silane linkage terminated with 1,3-dithiane via differential anodic oxidation of 1,3-dithiane. We found that the surface groups resulting from the anodic oxidation reaction differed according to the concentration of H₂O in the electrolyte solution during the oxidation reaction. The differential anodic oxidation was used successfully for the orthogonal immobilization of two different proteins. We demonstrated also the preparation of an immunoassay platform via orthogonal immobilization, which was then used to detect multiple target antigens based on a sandwich immunoassay.     

Palladium-catalyzed, asymmetric Mizoroki-Heck reaction of benzylic electrophiles using phosphoramidites as chiral ligands

We report herein the first examples of asymmetric Mizoroki-Heck reactions using benzyl electrophiles. A new phosphoramidite was identified to be an effective chiral ligand in the palladium-catalyzed reaction. The reaction is compatible with polar functional groups and can be readily scaled up. Several cyclic olefins worked well as olefin components. Thirty-one examples are included.     

Photocaging strategy for functionalisation of oligonucleotides and its applications for oligonucleotide labelling and cyclisation

We have used a photocaging strategy to develop novel phosphoramidites and expand the repertoire of protecting groups for modification of oligonucleotides by solid-phase synthesis. We synthesised five photolabile phosphoramidites and four new photolabile controlled pore glasses (CPGs). By using these photolabile phosphoramidites and CPGs, modified oligodeoxynucleotides (ODNs) with phosphate, amine, acid, thiol and carbonyl moieties at 5' and/or 3' ends were readily synthesised. To the best of our knowledge, this is the first report of introducing a carbonyl at the 5' end and thiol groups at both ends of ODNs with photolabile modifiers. Terminal labelling was also easily realised in solution or by on-column solid-phase synthesis. By using the photolabile amine modifier and the photolabile acid CPG, cyclisation of an oligodeoxynucleotide was achieved with good yields. This study provides an alternative way to introduce functional groups into oligonucleotides and expand the scope of oligonucleotide bio-orthogonal labelling.     

Metal-free oxidation of secondary benzylic alcohols using aqueous TBHP

We report a simple, yet efficient metal-free oxidation of secondary benzylic alcohols in the presence of t-butyl hydroperoxide (70% TBHP) with high yields of up to 98%. This type of reaction can be carried out using a wide variety of substrates, requires no other organic solvent, and proves to be tolerant toward a variety of different functional groups.     

Synthesis and characterization of covalently linked multilayer films prepared in the absence of solvent

We report the preparation of multilayer organic thin films prepared by sequential vapor-phase coupling of monomers. The reactions were carried out at room temperature and atmospheric pressure. Films prepared using up to six sequential coupling reactions are reported. The following specific vapor-phase reactions were found to be viable: reactions between acid chlorides and both aliphatic and aromatic amine, hydrolysis reactions, anhydride activation, and reactions between anhydrides and primary amines. Homobifunctionalized monomers, such as hexamethylenediamine, react primarily via a single endgroup rather than cross coupling to the reactive surface via both reactive groups. The estimated coverage of the multilayer films is between 36 and 46%. The films were characterized using ellipsometric, contact angle, and spectroscopic measurements.     

Facile synthesis of dendrimers combining aza‐Michael addition with Thiol‐yne click chemistry

We report a highly efficient approach to prepare dendrimers by taking advantage of the orthogonal characteristic of aza‐Michael addition and thiol‐yne reactions. A fifth generation dendrimer was synthesized within five steps without protection/activation procedures. The reactions proceed under benign conditions without byproducts, and the target products can be easily purified via extraction or precipitation without chromatography. The structure of each generation dendrimer was characterized using NMR spectroscopy, size exclusion chromatography, and mass spectrometry. The obtained dendrimers can have peripheral amine or alkyne groups. We demonstrated that these groups can be used for selective and specific conjugation with various functional groups. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2013