Ana Paula Esteves

Antimicrobial and demelanizing activity of Ganoderma lucidum extract, p-hydroxybenzoic and cinnamic acids and their synthetic acetylated glucuronide methyl esters

Mushroom extracts or isolated compounds may be useful in the search of new potent antimicrobial agents. Herein, it is described the synthesis of protected (acetylated) glucuronide derivatives of p-hydroxybenzoic and cinnamic acids, two compounds identified in the medicinal mushroom Ganoderma lucidum. Their antimicrobial and demelanizing activities were evaluated and compared to the parent acids and G. lucidum extract. p-Hydroxybenzoic and cinnamic acids, as also their protected glucuronide derivatives revealed high antimicrobial (antibacterial and antifungal) activity, even better than the one showed by commercial standards. Despite the variation in the order of parent acids and the protected glucuronide derivatives, their antimicrobial activity was always higher than the one revealed by the extract. Nevertheless, the extract was the only one with demelanizing activity against Aspergillus niger. The acetylated glucuronide derivatives could be deprotected to obtain glucuronide metabolites, which circulate in the human organism as products of the metabolism of the parent compounds.

Electroreductive cyclisation of unsaturated halides catalysed by nickel macrocyclic complexes

Abstract The indirect electroreduction of unsaturated aliphatic halides using Ni(II) complexes as electron-transfer mediators is achieved in N,N′ -dimethylformamide by constant current electrolysis between a cathode and a sacrificial anode in a diaphragmless cell. Cyclic compounds are obtained in low to high yields in conditions that avoid the usual preparation using organotin reagents.

Electrochemical intramolecular cyclisation of propargyl bromoethers catalysed by nickel complexes

The electrochemical intramolecular cyclisation of propargyl 2-bromoethers 1–3 in N,N′-dimethylformamide at constant current in a diaphragmless cell has been developed using NiII complexes as electron-transfer mediators. During controlled-current electrolyses of solutions of NiII complexes in the presence of bromoethers, catalytic reduction of the latter proceeds via one-electron cleavage of the carbon–bromine bond to form a radical intermediate that undergoes cyclisation to afford the cyclic compounds in moderate to good yields.

Reductive cyclisation of propargyloxy and allyloxy α-bromoester derivatives using environmentally friendly electrochemical methodologies

The electrochemical intramolecular cyclisation of α-bromo propargyloxy (1 and 2) and allyloxy (3) esters was carried out in ethanol and in ethanol–water mixtures as environmentally friendly systems using Ni(II) complexes as the catalysts. The reduction of the substrates proceeds via one-electron cleavage of the carbon–bromine bond to form a radical-type intermediate that undergoes cyclisation to afford cyclic ethers in moderate to good yields.

Synthesis of novel psoralen analogues and their in vitro antitumor activity

New tetracyclic benzofurocoumarin (benzopsoralen) analogues were synthesized and their inhibitory effect on the growth of tumor cell lines was evaluated. The human tumor cell lines used were MDA MB231 (breast adenocarcinoma), HeLa (cervix adenocarcinoma) and TCC-SUP (bladder transitional cell carcinoma). The in vitro antitumor activity of the new benzopsoralens was discussed in terms of structure-activity relationship. Molecular docking studies with human-CYP2A6 enzymes were also carried out with the synthesized compounds in order to evaluate the potential of these compounds to interact with the heme group of the enzymes. The results have demonstrated that the linear compounds have the most pronounced activity against tumor cell lines and this might be related to the better accessibility that these compounds have to the active site in relation to the angular ones that have shown in the majority of the cases multiple binding poses in the active site of CYP2A6.

Synthesis of esters derived from 2,3,4-tri-O-benzyl-alpha-D-methylglucoside

FCT (Fundacao para a Ciencia e Tecnologia) and FEDER for financial support. The Bruker Avance III 400 spectrometer is part of the National NMR network and was purchased under the framework of the National Programme for Scientific Reequipment, contract REDE/1517/RMN/2005, with funds from POCI 2010 (FEDER) and (FCT). We are also grateful for research grant VZ MSMT- 0021627501, Czech Republic.

Synthesis and allylic reactivity of α-bromomethyl β-(2,3,4,6-tetra-O-acetyl-β-d-glucopyranosyl)oxy α,β-unsaturated carbonyl compounds

Abstract Under radical conditions, N -bromosuccinimide converts α-methyl β-(2,3,4,6-tetra- O -acetyl-β- d -glucopyranosyl)oxy α,β-unsaturated carbonyl compounds into their α-bromomethyl derivatives. The bromides undergo nucleophilic displacement reactions without rearrangement with azide, O -ethyl dithiocarbonate and thiocyanate anions; with acetate anion, there is a preference for the formation of rearranged acetates with reasonable stereoselection.

Synthesis of Novel Glycoconjugates Derived From Alkynyl Heterocycles through a Click Approach

Abstract The synthesis of a series of novel 1,4-disubstituted 1,2,3-triazole compounds bearing a D-glucose derivative and an heteroaromatic system is described. Alkylation of isatin, 3-methyl-carbazole, and one tetrahydro-γ-carboline with propargyl bromide gave their N-propargyl derivatives in good yields. These compounds further reacted with acetylated D-glucose with the azide group in position 1 to give three final products and with peracetylated 6-azido-6-deoxy-α-D-methylglucoside, giving the corresponding derivative of tetrahydro-γ-carboline. Supplemental materials are available for this article. Go to the publishers online edition of Synthetic Communications® to view the free supplemental file. GRAPHICAL ABSTRACT

Reductive intramolecular cyclization of D-glucose-based unsaturated substrates by indirect electrochemical approach in “Green” media

Radical cyclisation continues to be a central methodology for the preparation of natural products containing heterocyclic rings. Hence, some electrochemical results obtained by cyclic voltammetry and controlled-potential electrolysis in the study of electroreductive intramolecular cyclisation of ethyl (2S, 3R)-2bromo-3-propargyloxy-3-(2’,3’,4’,6’-tetra-O-acetyl-β-D-glucopyranosiloxy) propanoate (1) promoted by (1,4,8,11-tetramethyl1,4,8,11-tetraazacyclotetra-decane)nickel(I), [Ni(tmc)], electrogenerated at glassy carbon cathodes in ethanol and ethanol/water mixtures containing tetraalkylammonium salts, are presented. During controlled-potential electrolyses of solutions containing [Ni(tmc)] and acetylated D-glucose-based bromo propargyl ester (1) catalytic reduction of the latter proceeds via one-electron cleavage of the carbon–bromine bond to form a radical intermediate that undergoes cyclization to afford the substituted tetrahydrofurans.

Synthesis and structural aspects of some intermediates in furofuran lignan synthesis

The synthesis of some intermediates of furofuran lignans was accomplished by a chemical cyclisation reaction using N-ethylpiperidine hypophosphite and azobisisobutyronitrile. This reaction afforded the 5-exo-dig cyclic compound as the major product along with another isomeric cyclic compound which possess an endocyclic double bond. A brief discussion is presented to explain the formation of these isomeric cyclic compounds by a base-catalysed tautomerism mechanism. Some structural aspects are discussed based on nuclear magnetic resonance data.