Lucio Toma

Enzymic acylation of sugars. Rationale of the regioselective butyrylation of secondary hydroxy groups of D- and L-galacto and mannopyranosides

Abstract Methyl 6-O-butyryl-α-D- and -L-galactopyranoside and methyl 6-O-butyryl-α-D- and -L-mannopyranoside, which present three contiguous secondary hydroxy groups in different orientations, have been acylated using three hydrolytic enzymes. Porcine pancreatic, Candida cylindracea, and Pseudomonas fluorescens lipases in organic solvents. Some generalization of the obtained results is discussed. Methyl 6-O-butyryl-α-D- and -L-galactopyranoside and methyl 6-O-butyryl-α-D- and -L-mannopyranoside, which present three contiguous secondary hydroxy groups in different orientations, have been acylated using three hydrolytic enzymes. Porcine pancreatic, Candida cylindracea, and Pseudomonas fluorescens lipases in organic solvents. Some generalization of the obtained results is discussed.

Solvent effect as the result of frontier molecular orbital interaction. V. Diels-Alder with heterodienophiles: a unified approach to the solvent effect of the Diels-Alder reactions☆

Abstract The solvent effect of Diels-Alder (D.A.) reactions with heterodienophiles was measured in several solvents. The rate of the reaction between 2,3-dimethylbutadiene (DMB) and diethylazodicarboxylate increases with the increases in the Acceptor Number of the solvent which behaves as an electrophile. The rate of the reaction between DMB and p. bromonitrosobenzene shows a small solvent effect which correlates with the cohesive pressure (δH2) of the solvent. The rate of the reactions between DMB and tetrachloro- or tetrabromo-o.benzoquinones give an inverse linear relationship with Dπ basicity parameters, thus rate decreases with increases in the nucleophilic character of the solvent..p]These monoparametric correlations (alternatively obtained with electrophilic, nucleophilic or cohesive pressure parameters of the solvent) rationalize the solvent effect of D.A. reactions reported in the literature, which fit one of the above reported three classes. The same result is obtained if the Kamlet-Taft multiparametric equation is applied to the same set of reactions. The main contribution remains that outlined with the monoparametric approach and some secondary effects or some borderline cases are usefully focussed

The opioid-receptor-like 1 (ORL-1) as a potential target for new analgesics.

Anew sequence, which encoded a novel G protein-coupled receptor, was disclosed by two different groups, using the nucleic acid probes based on the delta opioid receptor, first cloned in 1992. The new receptor, which Meunier called opioid-receptor-like 1 (ORL-1), was shown to share high homology with the opioid receptors and therefore thought to be a potential target for new analgesics. In this respect, the present review reports on the literature referring to ORL-1, to its natural ligand (nociceptin or orphanin FQ) and to several synthetic analogues recently described, both as agonists or antagonists at the receptor.

Synthesis of C-glycosyl compounds by the wittig iodocyclization procedure. Differences from mercuriocyclization

Abstract Various sugars were C -glycosylated by treatment with methylenetriphenyl-phosphorane and subsequent iodocyclization of the resulting hept- and hex-enitols. In all cases, a C glycofuranosyl compound was obtained, except for 3,4,5,7-tetra- O -benzyl-1,2-dideoxy- d - manno -hept-1-enitol which yielded a C -pyranosyl compound. High stereoselectoin, with formation of the 1,2- cis adduct as major product, was observed when an asymmetric center was present in the position adjacent to the double bond.

1,2-Dideoxy-3,4:5,7-bis-O-(1-methylethylidene)-D-gluco- and D-galacto-hept-1-ynitols: synthesis and conformational studies

Abstract 1,2-Dideoxy-3,4:5,7-bis- O -(1-methylethylidene)-D- gluco - and D- galacto -hept-l-ynitols were synthesized starting respectively from benzyl α,β-D-glucopyranoside and from benzyl α,β-D-galactopyranoside by bis-acetonidation, hydrogenolysis, Wittig reaction with chloromethylenetriphenylphosphorane, and dehydrohalogenation. The structures of the obtained compounds were confirmed by the NMR spectrocopic data which also allowed to determine the conformations of the molecules.

C-glycosides through the Wittig-cyclization procedure: observations on the influence of the nature of the substrate

Abstract The Moffatt C-glycosidation procedure was examined on different pyranoses; in glycopyranoses competitive elimination was observed in the Wittig reaction; all the other glycopyranoses investigated gave the Wittig product without elimination.

Fungal metabolites XXVI: The structure of saponaceolides B, C and D, new C-30 terpenoids from Tricholoma saponaceum☆

Abstract The structures of saponaceolides B, C and D, new C-30 terpenoids from Tricholoma saponaceum, have been established, including their absolute configuration. High cytotoxic activity was detected for saponaceolides B and C.

Merging and bifurcation of 4+2 and 2+4 cycloaddition modes in the archetypal dimerization of butadiene. A case of competing bispericyclic, pericyclic and diradical paths

The dimerization of butadiene has been explored by using DFT methods at the B3LYP level with the 6-311+G** basis set. A concerted bispericyclic TS for the endo pathway and a concerted pericyclic TS for the exo pathway are the lowest passes for the dimerization and occur at almost the same energy thus accounting for the lack of stereochemical preferences in the dimerization. Diradical paths involving two unswitched transoid butadiene moieties are competing and account for the formation of minor amounts of trans-1,2-divinyl cyclobutane and 1,5-cycloctadiene.

Inhibitory effects of fatty acid monoesters of 2-O-β-d-glucosylglycerol on Epstein–Barr virus activation

In a screening for cancer chemopreventing agents several glycosylglycerols were found to be active. In order to optimize the anti-tumor activity of this class of compounds, a series of 1-O-acyl-2-O-beta-D-glucopyranosyl-sn-glycerols differing in the acyl chain length, which varied from C4 to C18, were examined for their in vitro anti-tumor promoting effects on Epstein-Barr virus early antigen (EBV-BA) activation induced by the tumor promoter 12-O-tetradecanoylphorbol-13-acetate (TPA). Among the compounds tested, the monohexanoyl derivative was the most active and, noteworthy, the most potent compound of the glycosylglycerol series hitherto known.

1-O-, 2-O- and 3-O-β-glycosyl-sn-glycerols: Structure - anti-tumor-promoting activity relationship

Abstract The inhibitory activity of synthetic glycosylglycerols on Epstein-Barr virus early antigen (EBV-EA) activation was evaluated. Among the series of 1- O -, 2- O - and 3- O - glycosylglycerols tested, 1- O - β -D-galactopyranosyl- sn -glycerol showed the highest inhibitory effect toward promotion.