“Quick and click” assembly of functionalised indole rings via metal-promoted cyclative tandem reactions

An efficient and convenient synthesis of a variety of decorated indoles using a three-component tandem metal-catalysed process is described.

One-pot synthesis of amides from aldehydes and amines via C-H bond activation

A one-pot synthesis of amides from aldheydes with N-chloroamines, prepared in situ from amines, has been developed. Both aliphatic and aromatic aldehydes and many types of mono- and disubstituted amines are tolerant in this transformation. This cross-coupling reaction appears simple and convenient, has a wide substrate scope and makes use of cheap, abundant, and easily available reagents.

Angeli−Rimini's Reaction on Solid Support: A New Approach to Hydroxamic Acids

Angeli-Rimini's reaction has been performed for the first time on solid phase. A convenient one-step procedure for the synthesis of hydroxamic acids starting from aldehydes and solid-supported N-hydroxybenzenesulfonamide is reported. The hydroxamates are isolated in good to high yields and purities by simple evaporation of the volatile solvents, after treatment of the crude reaction mixture with sequestering agents.

Peptide nucleic acids (PNAs), a chemical overview

Peptide nucleic acid (PNA) is a nucleic acid analogue and a fully synthetic DNA/RNA-recognising ligand with a neutral peptide-like backbone. In spite of the large change on the backbone structure, PNA molecules bind strongly to complementary DNA and RNA sequences. Originally conceived as ligand for the recognition of double stranded DNA, the unique physico-chemical properties of PNAs have led to the development of a variety of research and diagnostic assays. The extraordinary properties of PNA may advance routine clinical tests and environmental analyses that will utilise the PNA technology. PNAs may also have an impact on in situ hybridisation, cytogenetics and industrial microbiology. This paper presents some recent achievements on peptide nucleic acids and discusses, from the viewpoint of literature, what the potential is and what the limitations of such compounds are. This review, which is not intended to be exhaustive, is mostly aimed at the current progress in PNA chemistry, structure, and hybridisation, highlighting some applications too.

Synthesis of 1-Alkyl-4-imidazolecarboxylates: A Catch and Release Strategy

The novel alkyl N-methyl-N-polystyreneamino-2-isocyanoacrylate was used for the synthesis of 1-substituted imidazole-4-carboxylates utilizing a "catch and release" methodology. The reactions were performed under microwave irradiation, affording the title compounds in both high yields and chemical purity directly to solution, from the solid phase support.

Microwave-Assisted Synthesis of Isonitriles: A General Simple Methodology

[reaction: see text] A facile conversion of formamides to isonitriles under very mild conditions and microwave irradiation is described. This simple and efficient method has been applied for the synthesis of both aliphatic and aromatic isonitriles in high yields.

A new polymer-supported reagent for the synthesis of beta-lactams in solution

A modified Mukaiyama reagent was prepared on a PS-DVB resin. This reagent was used for the preparation of beta-lactams, using the Staudinger reaction. The products were obtained by generating the ketene from a carboxylic acid under sonication with the resin followed by reaction with the imine. Excess of the imine was removed by reduction followed by acid scavenging.

New Cellulose-Supported Reagent: A Sustainable Approach to Guanidines

[reaction: see text] A new cellulose-supported reagent for the synthesis of guanidine in aqueous medium is reported starting from commercially available functionalized cellulose beads. Primary and secondary amines, anilines, and amino acids were transformed to the corresponding guanidines in high yields and under very mild conditions.

A New Polymer-Supported Reagent for the Synthesis of β-Lactams in Solution

A modified Mukaiyama reagent was prepared on a PS-DVB resin. This reagent was used for the preparation of beta-lactams, using the Staudinger reaction. The products were obtained by generating the ketene from a carboxylic acid under sonication with the resin followed by reaction with the imine. Excess of the imine was removed by reduction followed by acid scavenging.

Colorimetric Tools for Solid-Phase Organic Synthesis

One of the unresolved problems of solid-phase organic synthesis (SPOS) is the availability of general and rapid methods to monitor the transformation of functional groups present in molecules supported on insoluble supports. Color tests, far from providing the ultimate solution, may help in detection (and sometimes in quantification) of different functional groups. In this short review, we have collected most of the methods available and applied in SPOS with an Experimental Section that describes the procedure we have successfully applied to bead analyses in our laboratories.

A “Catch and Release” Strategy for the Parallel Synthesis of 2,4,5-Trisubstituted Pyrimidines

A resin capture and release strategy for making a combinatorial array of 2,4,5-trisubstituted pyrimidines is demonstrated by capturing beta-ketoesters and beta-ketoamides on a solid-supported piperazine. Through a cyclocondensation reaction, the solid-supported enaminone is reacted with several guanidines under heating or microwave irradiation affording the corresponding pyrimidines in good yield and chemical purity directly on solution. After this final step, the support can be effectively recycled.

Simple one-flask method for the preparation of hydroxamic acids

[reaction: see text] A one-step conversion of carboxylic acids to hydroxamic acids under very mild conditions is described. This simple and efficient method has been applied for the synthesis of enantiopure hydroxamate of alpha-amino acids and peptides.

Cellulose beads: a new versatile solid support for microwave- assisted synthesis. Preparation of pyrazole and isoxazole libraries

The synthesis of libraries of substituted pyrazoles and isoxazoles has been developed via in situ generation of polymer-bound enaminones. The synthetic protocol makes use of commercially available aniline cellulose, a low-cost and versatile biopolymer, under very mild conditions. This new support allowed us to carry out reactions in polar solvents under both conventional heating and MW irradiation without degradation of the polymer. The reaction between cellulose-bound enaminone and hydroxylamine or hydrazines to afford the target heterocycles in high yields directly in solution is the key step. The support can be conveniently recycled.

Trichloroisocyanuric/TEMPO oxidation of alcohols under mild conditions: a close investigation

Efficient oxidation of primary alcohols to the corresponding carboxylic acids can be carried out at room temperature and in acetone/water, using trichloroisocyanuric acid (TCCA) in the presence of catalytic TEMPO. The mild conditions of this procedure and the total absence of any transition metal make this reaction suitable for safe laboratory use. A possible mechanism is presented and discussed.

Beckmann rearrangement of oximes under very mild conditions

A variety of ketoximes, easily prepared from the corresponding ketones, undergo the Beckmann rearrangement upon treatment with 2,4,6-trichloro[1,3,5]triazine in N,N-dimethylformamide at room temperature in excellent yields. This procedure can be applied to aldoximes for obtaining the corresponding nitriles.

Mild and highly selective formyl protection of primary hydroxyl groups

Efficient conversion of primary alcohols to the corresponding formate esters can be carried out at room temperature in methylene chloride, using 2,4,6-trichloro-1,3,5-triazine and N,N-dimethylformamide in the presence of lithium fluoride. This procedure appears as a valid method for selectively protecting primary hydroxyl groups.

An efficient route to alkyl chlorides from alcohols using the complex TCT/DMF

[reaction: see text] Efficient conversion of alcohols and beta-amino alcohols to the corresponding chlorides (and bromides) can be carried out at room temperature in methylene chloride, using 2,4,6-trichloro[1,3,5]triazine and N,N-dimethyl formamide. This procedure can also be applied to optically active carbinols.

A very mild and chemoselective oxidation of alcohols to carbonyl compounds

Efficient oxidation of primary alcohols and beta-amino alcohols to the corresponding aldehydes and alpha-amino aldehydes can be carried out at room temperature and in methylene chloride, using trichloroisocyanuric acid in the presence of catalytic TEMPO: aliphatic, benzylic, and allylic alcohols, and beta-amino alcohols are rapidly oxidized without no overoxidation to carboxylic acids. Secondary carbinols are slowly oxidized so that the reaction is highly chemoselective. Reaction: see text.

A simple preparation of ketones. N-protected alpha-amino ketones from alpha-amino acids

[reaction: see text] Carboxylic acids and amino acids are readily converted, under mild conditions, into the corresponding activated esters, which are reacted with Grignard/CuI reagent to give the corresponding ketones in nearly quantitative yields. The compounds were recovered substantially pure from the reaction mixtures.

Small ring constrained peptidomimetics. Synthesis of epoxy peptidomimetics, inhibitors of cysteine proteases

Different dipeptide analogues containing an oxirane ring in the place of the peptidic bond were prepared starting from naturally occurring amino acids. N-Fmoc-amino aldehydes were transformed into the corresponding methoxyvinyl derivatives through a Wittig reaction, and the addition of PhSeCl gave a series of different alpha-phenylselenyl aldehydes. Mukajiama reaction with silylketene acetals gave an intermediate product that was finally transformed into the desired oxiranyl peptidomimetics. Following this strategy we were able to control three new contiguous stereocenters starting from the enantiomerically pure amino acid. The dipeptide analogues could be used in SPPS on a SASRIN resin as the final epoxides were relatively unstable under acidic conditions. Moreover the synthesis of the single dipeptide mimetics was carried out on solid phase to generate a small library of epoxy peptidomimetics. Some of the products prepared in this work resulted as time-dependent reversible inhibitors of cysteine protease.