Microwave-assisted synthesis of novel purine nucleosides as selective cholinesterase inhibitors.

Alzheimer's disease (AD), the most common form of senile dementia, is characterized by high butyrylcholinesterase (BChE) levels in the brain in later AD stages, for which no treatment is available. Pursuing our studies on selective BChE inhibitors, that may contribute to understand the role of this enzyme in disease progression, we present now microwave-assisted synthesis and anticholinesterase activity of a new nucleoside series embodying 6-chloropurine or 2-acetamido-6-chloropurine linked to D-glucosyl, D-galactosyl and D-mannosyl residues. It was designed to assess the contribution of sugar stereochemistry, purine structure and linkage to the sugar for cholinesterase inhibition efficiency and selectivity. Compounds were subjected to Ellman's assay and their inhibition constants determined. The α-anomers were the most active compounds, while selectivity for BChE or acetylcholinesterase (AChE) inhibition could be tuned by the purine base, by the glycosyl moiety and by N(7)-ligation. Some of the nucleosides were far more potent than the drug galantamine, and the most promising competitive and selective BChE inhibitor, the N(7)-linked 2-acetamido-α-D-mannosylpurine, showed a Ki of 50 nM and a selectivity factor of 340 fold for BChE over AChE.

Facile synthesis of oxo-/thioxopyrimidines and tetrazoles C-C linked to sugars as novel non-toxic antioxidant acetylcholinesterase inhibitors.

Microwave-assisted synthesis of oxo-/thioxopyrimidines and tetrazoles linked to furanoses with D-xylo and D-ribo configuration, and to a D-galacto pyranose is reported and compared to conventional methods. Reaction of dialdofuranoses and dialdopyranoses with a ß-keto ester and urea or thiourea under microwave irradiation at 300 W gave in 10 min the target molecules containing the 2-oxo- or 2-thioxo-pyrimidine ring in high yield. The tetrazole-derived compounds were obtained in two steps by reaction of the formyl group with hydroxylamine hydrochloride, copper sulfate, triethylamine and dicyclohexylcarbodiimide to give an intermediate nitrile, which was then treated with sodium azide. The use of microwave irradiation in the latter step also resulted in a considerably shorter reaction time (10 min) compared to hours under conventional heating to obtain a complete starting materials conversion. Acetylcholinesterase inhibition ranged from 20% to 80% for compounds concentration of 100 µg/mL, demonstrating the potential of this family of compounds for the control of Alzheimer's disease symptoms. Most of the compounds showed antioxidant activity in the ß-carotene/linoleic acid assay, some of them exhibiting IC(50) values in the same order of magnitude as those of gallic acid. The bioactive compounds did not show cytotoxic effects to human lymphocytes using the MTT method adapted for non-adherent cells, nor genotoxicity determined by the short-term in vitro chromosomal aberration assay.

Structural characterisation of flavonoids and flavonoid-O-glycosides extracted from Genista tenera by fast-atom bombardment tandem mass spectrometry.

Genista tenera is a plant native to the Madeira Island (Portugal). From the ethanol extract of its powdered aerial parts, two flavones, three isoflavones and one 7-O-glucosyl isoflavone were isolated. A mass spectrometric study of these compounds was performed using liquid secondary ion mass spectrometry (LSIMS) in combination with high-energy collision-induced dissociation (CID) and tandem mass spectrometry (MS/MS). Characteristic fragmentation patterns were observed in all the investigated compounds; the loss of small neutral species from the protonated molecules was useful for identifying the presence of specific functional groups in the A- and B-rings. In order to help to establish the proposed structures, NMR and UV studies were also performed.

Bioactive humulene derivatives from Asteriscus vogelii.

The bioactive fractions obtained from the extract of Asteriscus vogelii afforded a new humulene derivative, the 8-oxo-6,7,9,10-tetrahydrohumulen-1,12-olide (1), in addition to the known asteriscunolides A (2), C (3) and D (4), and the acids 8-oxo-alpha-humula-6Z,9Z-dien-12-oic acid (5), 8-oxo-alpha-humula-6E,9Z-dien- 12-oic acid (6) and 8-oxo-alpha-humula-6E,9E-dien-12-oic acid (7), characterized as their methyl esters. Evaluation of their phytotoxic and cytotoxic activities was accomplished. Compounds 3 and 4 gave the highest inhibition of plant cell cultures and of the plant Lemna paucicostata. Compound 4 was also the most active against P-338 lymphoma in mice, A-549 carcinoma of human lung, HT-29 carcinoma of human colon and MEL-28 human melanoma.

Synthesis of pseudo-C-nucleosides.

Whereas the reaction of 1,2-O-isopropylidene-alpha-D-xylo-5-hexulofuranuronamide (1) with the Wittig reagent ethoxycarbonylmethylenetriphenylphosphorane gave 3-(1,2-O-isopropylidene-beta-L-threofuranos-4-yl)maleimide (2, 15%) and ethyl 5-carbamoyl-5,6-dideoxy-1,2-O-isopropylidene-alpha-D-xylo-hept-5-enof uranuronate (3, 76%), a similar reaction of 3-O-benzyl-1,2-O-isopropylidene-alpha-D-ribo-5-hexulofuranuronamide++ + (4) gave only 3-(3-O-benzyl-1,2-O-isopropylidene-alpha-D-erythrofuranos-4-yl)mal eimide (5), 80%), and that of 3-O-benzyl-1,2-O-isopropylidene-alpha-D-xylo-5-hexulofuranuronamide++ + (6) gave only ethyl 3-O-benzyl-5-carbamoyl-5,6-dideoxy-1,2-O-isopropylidene- alpha-D-xylo-hept-5-enofuranuronate (7, 85%). The formation of the maleimide ring depended on the orientation and substitution of HO-3'. Compounds 2 and 5 are analogous of showdomycin.