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Reversible acetylcholinesterase (AChE) inhibitors are key therapeutic tools to modulate the cholinergic connectivity compromised in several degenerative pathologies. In this work, four alkyl esters of homarine were synthesized and screened by using Electrophorus electricus AChE and rat brain AChE-rich fraction. Results showed that all homarine alkyl esters are able to inhibit AChE by a competitive inhibition mode. The effectiveness of AChE inhibition increases with the alkyl side chain length of the homarine esters, being HO?C16 (IC50=7.57±3.32 μM and Ki=18.96±2.28 μM) the most potent inhibitor. The fluorescence quenching studies confirmed that HO?C16 is the compound with higher selectivity and affinity for the tryptophan residues in the catalytic active site of AChE. Preliminary cell viability studies showed that homarine esters display no toxicity for human neuronal SH-SY5Y cells. Thus, the long-chain homarine esters emerge as new anti-cholinesterase agents, with potential to be considered for therapeutic applications development.

We have developed a C2-selective mono-silylation of a variety of pyridines using a Rh-Al complex. Both the site- and mono-selectivity are controlledviathe pyridine coordination to the Lewis-acidic Al center prior to the activation of the pyridine C(2)-H bond at the proximal Rh center. A reaction mechanism is proposed based on several mechanistic studies, including the isolation of a (2-pyridyl)silylrhodium intermediate.

The ubiquitousness of esters and amide functionalities makes their coupling reaction one of the most sought-after organic transformations. Herein, we have described an efficient microwave-assisted synthesis of esters and amides. Soluble triphenylphosphine, in conjugation with molecular iodine, gave the desired products without the requirement for a base/catalyst. In addition, a solid-phase synthetic route is incorporated for the said conversion, which has added advantages over solution-phase pathways, such as low moisture sensitivity, easy handling, isolation of the product by simple filtration, and reusability. In short, our method is simple, mild, green, and highly chemoselective in nature.

The dehydration of aldoximes into nitriles has been performed in the presence of various metal oxides with different acid-base properties (Al2O3, TiO2, CeO2, MgO). The results showed that a nanocrystalline CeO2 was the most active catalyst. An in situ IR spectroscopy study supports a polar elimination mechanism in the dehydration of aldoxime on metal oxide catalysts, in which Lewis acid sites and basic sites are involved. The Lewis acid sites intervene in the adsorption of the oxime on the catalyst surface while surface base sites are responsible for the C1-H bond cleavage. Thus, the acid-base properties of nanocrystalline CeO2 are responsible for the high catalytic activity and selectivity. A variety of aldoximes including alkyl and cycloalkyl aldoximes have been dehydrated into the corresponding nitriles in good yields (80-97%) using nanosized ceria which moreover resulted in a stable and reusable catalyst. Additionally, it has been showed that a variety of pharmacologically important products such as picolinamide and picolinic acid alkyl ester derivatives can be obtained in good yields from 2-pyridinaldoxime in a one-pot process using the nanoceria as catalyst.

Nano sulfated titania was tested as catalyst for esterification of free fatty acids, specially methanolic and ethanolic esterification of stearic acid (biodiesels). Factorial design evidenced a positive effect of reaction temperature, amount of catalyst, and solvents on ester conversion. This nano-sized sulfated titania has been prepared by a sol-gel hydrothermal process. This prepared sulfated titania showed high catalytic activity in direct esterification of fatty acids as well as benzoic acids with various alcohols and phenols under solvent-free conditions. This method is of great value because of its environmentally benign character, easy handling, high yields, convenient operation, and green. FT-IR studies are shown that the catalyst can be reused for acylation without loss of catalytic activity.

CeO2 acted as an efficient and reusable heterogeneous catalyst for transesterification of esters with alcohols under the solvent-free conditions at 160 °C. Among the 11 kinds of metal oxides, CeO2 is the most suitable catalyst in terms of catalytic activity, leaching-resistance and reusability. This catalytic system tolerates various esters and alcohols, and valuable esters such as heteroaromatic esters and benzyl benzoates are produced, demonstrating a practical utility of the system. On the basis of kinetic analysis and in situ IR studies of adsorbed species, a reaction mechanism is proposed, in which proton abstraction of alcohol by a Lewis base site of CeO2 to yield alkoxide species is the rate-limiting step.

Thirteen kinds of metal oxides were tested for one-pot selective synthesis of esters from nitriles and alcohols. Ceria (CeO2) showed more than two orders of magnitude higher activity than the other oxides. CeO2 acted as a reusable and effective catalyst for the ester synthesis from various nitriles and alcohols under neutral and solvent-free conditions at 160 °C. This method provides a rare example for the synthesis of heteroaromatic esters, which have been difficult to synthesize by conventional catalytic esterification methods. Valuable esters such as picolinic acid alkyl esters and niacin benzyl esters were synthesized, demonstrating a practical aspect of the present method. Kinetic studies suggested the following reaction mechanism: (1) H2O and ROH dissociate on CeO2, (2) nucleophilic attack of hydroxyl species (OHδ-) to the adsorbed nitrile on CeO2, leading to the formation of the primary amide, (3) nucleophilic attack of alkoxide species (ORδ-) to the amide as the rate-limiting step.

An investigation on Mucor miehei lipase-catalyzed transesterifications of 16 aromatic and heteroaromatic esters in organic solvents is described. The points studied were the activity and regioselectivity of the enzyme-catalyzed reaction of either one or two ester groups situated in different positions on several heterocyclic systems with an aliphatic alcohol. The reactions took place in moderate to good yields and, in some cases, regioselectively.

By reaction of aromatic K-carboxylates having nucleophilic N-atom in solid-liquid phase transfer catalysis (PTC) conditions without added solvent (catalyst : tetraalkylammonium halide) with alkylating reagents, the corresponding esters are prepared.By a judicious choice of experimental conditions, the amounts of N-alkylated products can be lowered.From 2-pyrrolecarboxylic acid, the three isomers of pyridinecarboxylic acid and o-aminobenzoic acid, corresponding esters of ethyl, benzyl, n-octyl and n-cetyl, generally are obtained with good yields.