The worldwide urge to embrace a sustainable and bio-compatible chemistry has led industry and academia\ud to develop of chlorine-free methodologies focused on the use of CO2 and CO2-based compounds\ud as feedstocks, promoters and reaction media. In this scenario, dialkyl carbonates (DACs) and in particular\ud dimethyl carbonate (DMC) occupy a privileged position due to their low toxicity, high biodegradability and\ud peculiar reactivity. Nowadays, the large-scale production of DACs is carried out through clean processes\ud (i.e., phosgene-free processes), which include the direct insertion of CO2 into epoxides, allowing – in\ud principle – recycling of the carbon dioxide emitted during carbonate degradation. This groundbreaking\ud achievement has definitely drawn attention toward the conception of procedures to activate the rather\ud stable DACs with the aim of employing these compounds as green alternatives to their reactive chlorinated\ud analogues. DACs are ambident electrophiles, which under appropriate conditions can undergo\ud BAc2- or BAl2-nucleophilic substitution to give, respectively, alkoxycarbonylation and alkylation reactions.\ud The many efforts devoted to improving the industrial suitability of organic carbonates have unveiled an\ud intriguing and innovative chemistry as demonstrated by the numerous publications and patents published\ud on these compounds over the last thirty years. This review reports on DACs as alkoxycarbonylating agents\ud and their applications in industry and fine synthesis, as well as alkylating agents including allylic alkylation\ud using palladium catalysts and the Pd/Ti bimetallic system and anchimerically driven alkylations via mustard\ud carbonates. Moreover, the reactivity of organic carbonates toward several substrates and under different\ud reaction conditions is described along with some distinctive DAC-mediated cyclization and transposition\ud reactions. The synthesis of olefins and ethers under both liquid and gas phase conditions via thermal decarboxylation\ud of organic carbonates is also reported
A library of biofuel candidates, 2,5-bis(alkoxymethyl) furans (BAMFs), was prepared from 2,5-bis(hydroxymethyl)furan (BHMF) by etherification in mild conditions using the acid catalyst Purolite. The purification of the BAMFs has been assessed, and gram-scale experiments have been carried out for two specific examples. The efficiency of this synthetic approach to BAMFs was ascribed to the BHMF-activated structure and its interaction with the aromatic acid catalyst.
We report here a two step efficient route for the synthesis of 1,2,3,4-tetrahydro-β-carboline (THBC)-based tetracyclic peptidomimetics from a Ugi 4-CR/Pictet-Spengler reaction sequence. Suitably N-protected 2-aminoacetaldehyde was for the first time applied as the carbonyl component in a Ugi four-component reaction, opening the way to the employment of N-protected α-amino acid-derived aldehydes in the same role. The potential of the obtained scaffolds is related to the possibility of further derivatization with the desired pharmacophoric groups, on both the terminal acid and amine functional groups, for the development of conformationally constrained tryptophan-containing peptide ligands. Extensive molecular modeling and (1)H NMR studies highlighted a robust, folded, β-turn-like conformation for one of these peptidomimetic compounds.
Cyclic CNGRC (cCNGRC) peptides are very important targeting ligands for Aminopeptidase N (APN or CD13), which is overexpressed on the surface of many cancer cells. In this work we have (1) developed an efficient solid-phase synthesis and (2) tested on purified porcine APN and APN-expressing human cells two different classes of cCNGRC peptides: the first carrying a biotin affinity tag or a fluorescent tag attached to the carboxyl Arg-Cys-COOH terminus and the second with the tags attached to the amino H2N-Cys-Asn terminus. Carboxyl-terminus functionalized cCNGRC peptides 3, 6, and 8 showed good affinity for porcine APN and very good capacity to target and be internalized into APN-expressing cells. In contrast, amino-terminus functionalized cCNGRC peptides 4, 5, and 7 displayed significantly decreased affinity and targeting capacity. These results, which are in agreement with the recently reported X-ray structure of a cCNGRC peptide bound to APN showing important stabilizing interactions between the unprotected cCNGRC amino terminus and the APN active site, indicate that the carboxyl and not the amino-terminus of cCNGRC peptides should be used as a "handle" for the attachment of toxic payloads for therapy or isotopically labeled functions for imaging and nuclear medicine.
In this work, bio‐based platform molecule 5‐hydroxymethylfurfural (HMF) was synthesised under mild conditions (90 °C) from D‐fructose using as media a mixture of dimethyl carbonate:tetraethyl ammonium bromide (DMC:TEAB). This solvent system resulted in a efficient production of HMF in the presence of both Amberlyst‐15 (heterogeneous catalyst) and BF3O(Et)2 (homogeneous catalyst). HMF was recovered from the reaction mixture with or without minimal work‐up. It is noteworthy that this synthetic approach provided high yielding product also when performed in a large‐scale. Quick reduction of HMF to the related 2,5‐bis(hydroxymethyl)furan was also conducted to further confirm the proposed procedure. Besides, the materials efficiency metrics of the optimized DMC‐based synthetic approach have been compared to alternative syntheses for HMF reported in the literature. This latter study takes into consideration synthetic routes that employ D‐fructose as substrate, easy accessible catalysts and report detailed procedures and evidence of the isolation of HMF.
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