Alberto Arnone

Structures of melleolides B-D, three antibacterial sesquiterpenoids from Armillaria mellea

Abstract The structures of melleolides B-D, three new protoilludene sesquiterpenoid O-methylorsellinates isolated from a culture of Armillaria mellea , have been elucidated on the basis of chemical and spectral data.

Trifluoromethyl vs. methyl ability to direct enantioselection in microbial reduction of carbonyl substrates.

Abstract The stereoselective reduction of 3-trifluoromethylcyclohexanone ( 1a ), ( E )-1,1,1-trifluoro-4-phenyl-3-buten-2-one ( 3a ), and their unfluorinated analogues 1b and 3b has been performed with some growing microorganisms. Differences in the electronic and steric properties of the trifluoromethyl and methyl residues result in different chemo- and stereoselectivities in the microbial reduction of phenylbutenones 3a and 3b while cyclohexanones 1a and 1b showed strictly similar stereoselectivities. A new protocol based on 13 C NMR spectra of 2-phenylpropionic acid esters has been used to assign the absolute configuration of the obtained secondary alcohols.

Dimers of nicotinamide adenine dinucleotide: New evidence for the structure and the involvement in an enzymatic redox process

Abstract The composition and the structure of the product from the known electrochemical dimerization of the NAD+ have been conclusively demonstrated. A detailed analysis of the 1H and 13C nmr spectra has in fact led to the conclusion that the product contains three diastereoisomeric dimers of the 4,4′-tetrahydrobipyridyl type. Furthermore, the cytoplasmic fraction obtained from a standard mitochondrial preparation of rat liver has been shown to catalyze the oxygen uptake by the dimers. A 1 : 1 molar ratio of the reagents in the redox process is indicated by manometric data on oxygen uptake complemented by spectrophotometric analysis of the oxidized substrates, suggesting that H2O2 is the reduction product. NAD+ was identified as the oxidation product by an enzymatic method.

Total synthesis of a pepstatin analog incorporating two trifluoromethyl hydroxymethylene isosteres (Tfm-GABOB) and evaluation of Tfm-GABOB containing peptides as inhibitors of HIV-1 protease and MMP-9

Abstract We describe the asymmetric total synthesis of a trifluoromethyl (Tfm) analogue of the aspartate protease inhibitor pepstatin incorporating two γ-Tfm-γ-amino-β-hydroxybutyric acid (γ-Tfm-GABOB) units instead of the natural statine units. The title compound as well as several Tfm-substituted precursors were tested as inhibitors of HIV-1 protease and Gelatinase B (MMP-9)

Secondary mould metabolites. Part 47. Isolation and structure elucidation of clavilactones A–C, new metabolites from the fungus Clitocybe clavipes

Clavilactones A–C (1, 4 and 5) have been isolated from cultures of the Basidiomycetous fungus Clitocybe clavipes. Their structures and relative configurations have been deduced from 1H and 13C NMR studies, chemical reactions and single-crystal X-ray analysis of the dimethyl ether derivative 3. 1H–1H coupling constants, NOE data and molecular modelling calculations all suggest that the molecules have little conformational mobility and the conformation adopted in solution by clavilactone A 1 and dimethyl ether derivative 3 is essentially identical with that of 3 in the solid state. Clavilactones A–C exhibit antifungal and antibacterial activity and inhibit the growth germination of Lepidium sativum. A possible biogenetic origin of clavilactone A 1 is discussed.

Perylenequinones from cucumber seedlings infected with Cladosporium cucumerinum

Abstract The structure of cladochrome A, a perylenequinone pigment isolated from etiolated cucumber seedlings infected with fungal spores of Cladosporium cucumerinum, has been revised and established as that of a diester of 3-hydroxybutyric acid with ent-isophleichrome. Another pigment from the same source, cladochrome B, is the corresponding ester of ent-isophleichrome with 3-hydroxybutyric and benzoic acids.

Selectivities in the oxidation of tertiary amines and pyridine derivatives by perfluoro cis-2,3-dialkyloxaziridines

Abstract When tertiary amines 1 are reacted with perfluoro cis-2,3-dialkyloxaziridines 2 at −60°C corresponding N-oxides 3 are formed in high yields. The process is chemoselective and diastereoselective. The chemoselectivity in the reaction of alkenyl substituted pyridines is solvent dependent, attack occurring exclusively at the carbon-carbon double bond or at the nitrogen atom under protic and aprotic conditions, respectively. Lower selectivities were obtained when standard reagents were used.

FLUORINATED ANALOGUES OF NOJIRIMYCIN AND MANNOJIRIMYCIN FROM A NON-CARBOHYDRATE PRECURSOR

Abstract 1,3,5-Trideoxy-3-fluoronojirimycin 3a and its 5-epi isomer 3b have been synthesized in enantiomerically pure form starting from the fluorohydroxysulfinylhexene (2R,3S,SS)-6. The nitrogen atom of the target bioactive compounds is introduced by replacing the sulfinyl group with an hydroxylamine residue and an intramolecular aminomercuration reaction builds up the desired piperidine ring. Finally, an oxidative demercuration affords the hydroxymethyl moiety. The same synthetic sequence allows to obtain 1,3,5-trideoxy-3-fluoromannojirimycin 4a and its 5-epi isomer 4b starting from the benzyloxy-fluorosulfinylhexene (2S,3S,RS)-7.

13C NMR analysis of anthraquinones as models for anthracycline Antibiotics

Abstract 9,10-Anthraquinone (9,10-AQ) and several derivatives have been analyzed by FT 13 C NMR spectroscopy. All the 13 C frequencies have been assigned; the one-bond coupling constants and some long-range interactions are reported. The effect of substituents OH, OMe, OAc, and COMe on the chemical shifts has been studied for monosubstituted and some 1,5- and 1,8-disubstituted compounds. The structure of 9,10-AQ is discussed on the basis of the comparison with the parent hydrocarbons, disubstituted benzenes, and naphthoquinone and benzoquinone. Intramolecular H bonding and tautomeric structures are also discussed.

A hydroxytetradecatrienoic acid from Mycosphaerella rubella

Investigations on the acidic fractions from extracts of a culture of Mycosphaerella rubella led to the isolation of a new unsaturated dihydroxy acid, 6,13-dihydroxytetradeca-2,4,8 trienoic acid, and two of its derivatives, which are probably artifacts. Their structures were determined on the basis of H and C NMR evidence. The absolute configuration of the chiral centres of the new acid was elucidated using the modified Moshers method.