Ines Mancini

Pyrolysis of cellulose catalysed by nanopowder metal oxides: production and characterisation of a chiral hydroxylactone and its role as building block

As a bulk component of plant biomass, cellulose plays a key role in the route leading to viable chemicals from renewable resources. Pyrolysis is a thermal treatment that converts cellulose into a liquid material (bio-oil) containing dehydrated monomers, among which the anhydrosugars levoglucosan (LGA) and levoglucosenone (LGO) have been widely investigated as chiral multifunctional synthons. A chiral cyclic hydroxylactone (LAC, 1) is also produced, but its potential as chemical intermediate has never been scrutinised, probably because it is generated only in minute amounts. In this study, experiments with a fixed bed reactor showed that the yields of LAC could be significantly increased by pyrolysing cellulose for few minutes at 350 °C in the presence of nanopowder (NP) titanium dioxide, aluminium oxide, and aluminium titanate (AlTi). When pyrolysis was conducted with NP AlTi at 500 °C, LAC became the principal anhydromonosaccharide and could be isolated from the resulting bio-oil with simple operations (6% overall yield). Its structure could be definitively assigned to the (1R,5S)-1-hydroxy-3,6-dioxabicyclo[3.2.1]octan-2-one by extensive NMR analysis and high resolution EI-MS experiments, providing a firm evidence of its previous attribution. The significance of LAC as building block for follow-up bioproducts was evaluated in some examples, including the synthesis of a suitable amide by the effective and eco-friendly microwave assisted methodology.

Synthesis and bioactivity of linear oligomers related to polymeric alkylpyridinium metabolites from the Mediterranean sponge Reniera sarai

Dimers and tetramers of linear 3-alkylpyridinium salts have been synthesized by an efficient synthetic pathway, which is also applicable to the preparation of higher oligomers. Mono-, di- and tetrameric compounds have been tested for antibacterial and hemolytic activities and for the inhibition of acetylcholinesterase and protein phosphatase 2A. Their activities were compared to those of the natural poly-3-octylpyridinium alkaloids isolated from the Mediterranean sponge Reniera sarai. Relatively high antibacterial and anti-acetylcholinesterase activities were observed that increase with higher degrees of oligomerization.

Hanishin, a Semiracemic, Bioactive C9 Alkaloid of the Axinellid Sponge Acanthella carteri from the Hanish Islands. A Shunt Metabolite?

The C9 alkaloid hanishin (2), isolated from a collection in the Hanish Islands (Red Sea) of the highly polymorphic sponge Acanthella carteri, has low enantiomeric purity and may be viewed as a shunt metabolite, albeit biologically active, from co-occurring oroidin (1).

Infrared spectroscopy of copper-resveratrol complexes: A joint experimental and theoretical study

Infrared multiple-photon dissociation spectroscopy has been used to record vibrational spectra of charged copper-resveratrol complexes in the 3500-3700 cm(-1) and 1100-1900 cm(-1) regions. Minimum energy structures have been determined by density functional theory calculations using plane waves and pseudopotentials. In particular, the copper(I)-resveratrol complex presents a tetra-coordinated metal bound with two carbon atoms of the alkenyl moiety and two closest carbons of the adjoining resorcinol ring. For these geometries vibrational spectra have been calculated by using linear response theory. The good agreement between experimental and calculated IR spectra for the selected species confirms the overall reliability of the proposed geometries.

Temperature Effect on the Vibrational Dynamics of Cyclodextrin Inclusion Complexes: Investigation by FTIR-ATR Spectroscopy and Numerical Simulation

The vibrational dynamics of solid inclusion complexes of the nonsteroidal anti-inflammatory drug Ibuprofen (IBP) with beta-cyclodextrin (beta-CD) and methyl-beta-cyclodextrin (Me-beta-CD) has been investigated by using attenuated total reflection-Fourier transform infrared FTIR-ATR spectroscopy, in order to monitor the changes induced, as a consequence of complexation, on the vibrational spectrum of IBP, in the wavenumber range 600-4000 cm(-1). Quantum chemical calculations were performed on monomeric and dimeric structures of IBP, derived from symmetric hydrogen bonding of the two carboxylic groups, in order to unambiguously assign some characteristic IR bands in the IBP spectrum. The evolution in temperature from 250 to 340 K of the C horizontal lineO stretching vibration, described by a best-fit procedure, allowed us to extract the thermodynamic parameter DeltaH associated to the binding of IBP with betaCDs in the solid phase. By comparing these results, Me-beta-CD has been shown to be the most effective carrier for IBP.

Almazole D, a new type of antibacterial 2,5-disubstituted oxazolic dipeptide from a red alga of the coast of Senegal

Abstract Almazole D ((+)-5), a potently antibacterial dipeptide from a delesseriacean seaweed collected at Almadies, North of Dakar, is a novel variant of 2,5-disubstituted oxazolic dipeptides conceivably deriving from oxidative deamination rather than decarboxylation of tryptophan.

3-Akylpyridinium and 3-Alkylpyridine Compounds from Marine Sponges, Their Synthesis, Biological Activities and Potential Use

Abstract During the last 30 years, a number of simple 3-alkylpyridine and 3-alkylpyridinium (3-AP) compounds have been isolated from marine sponges belonging to the order Haplosclerida, suggesting these compounds as chemical markers for systematic determination of haplosclerid sponges. They were isolated from haplosclerid sponges either as (i) monomers differing in the length, saturation, branching and termination of the alkyl chains, (ii) cyclic or linear oligomers, or (iii) a mixture of high-molecular weight polymers. What the biosynthetic pathways are in marine sponges, and how these compounds can be made by organic synthesis is also an interesting question addressed in our review. In this regard we focus particularly on organic syntheses by which selective polymerization of 3-alkylpyridinium polymers may be achieved. Structural investigation of alkylpyridinium compounds and the role played by mass spectrometry has also been reviewed. In spite of their relatively simple chemical structure, all these compounds exert a broad spectrum of biological activities. More than 40 monomeric 3-AP compounds have been isolated from marine sponges and the majority bear a nitrogenous functionality at the end of the alkyl chain. Almost all reported 3-AP monomers exert moderate cytotoxicity, in the concentration range of a few micrograms per millilitre, against certain transformed cell lines. An example of 3-alkylpyridines is niphatyne A, from the marine sponge of the genus Niphates which exhibits an IC 50 of 0.5 μg/mL against several transformed cell lines. The majority of 3-AP dimers and trimers were isolated from haplosclerid sponges in cyclic forms. Haliclamines are a typical representative of this group. They inhibit the division of fertilized sea urchin eggs as well as the growth of several transformed cell lines. On the other hand cyclostellettamines are typical example of cyclic alkylpyridinium dimers that modulate muscarinic receptors. Recently an increasing number of polymeric alkylpyridinium compounds have been isolated from haplosclerid sponges. Halitoxins, amphitoxins and alkylpyridinium salts from Mediterranean sponge Reniera sarai are the most studied. The latter exhibit a plethora of interesting biological activities. For instance, they are able to make pores in membranes through which DNA can be transfected into the cell, show selective cytotoxic activity against certain human cancer cells and possess non-toxic inhibitory antifouling properties against larvae of several important fouling organisms. The biological activities and potential use of alkylpyridinium polymers are discussed.

Antisettlement activity of synthetic analogues of polymeric 3-alkylpyridinium salts isolated from the sponge Reniera sarai

Based on the high, non-toxic and reversible antifouling activity of the polymeric 3-alkylpyridinium salts isolated from the sponge Reniera sarai, the anti-settlement activity and toxicity of a series of synthetic analogues has been studied. All the test compounds were less efficient than the natural polymers, suggesting that the high and reversible anti-macrofouling activity of the natural polymers could derive from their detergent-like properties. The values obtained for EC50sett. of inhibition of cyprid settlement and EC50imm. as naupliar toxicity for the synthetic compounds indicate that the presence of single or multiple charges in the structure is not relevant for the antifouling activity which, conversely, is favoured by increasing the length of the alkyl chain, or by the presence of uncharged pyridine units. The compound 1,8-di(3-pyridyl)octane was the most efficient (EC50sett.= 0.44 μg ml–1), although with a higher toxicity on naupliar stage of B. amphitrite than the natural polymers.

Computational NMR spectroscopy of organoarsenicals and the natural polyarsenic compound arsenicin A.

The (1)H and (13)C NMR chemical shifts and coupling constants of a series of organoarsenic compounds were calculated with DFT methods and compared with available experimental spectra. We show that non-relativistic methods successfully model the NMR spectra of these molecules; relativistic spin-orbit effects are small but appreciable for (13)C shifts, and their inclusion is beneficial. Application of the same methods of calculation to the intriguing natural polyarsenic compound arsenicin A allowed several viable alternative structures to be ruled out and thereby confirmed the previously suggested adamantane-like structure of arsenicin A. These results not only reinforce the known predictive power of DFT NMR calculations, but also open the way for the investigation of other naturally occurring molecules with unusual structures outside the scope of empirical methods.

STEREOCHEMICAL FEATURES OF SESQUITERPENE METABOLITES AS A DISTINCTIVE TRAIT OF RED SEAWEEDS IN THE GENUS LAURENCIA

Abstract Red seaweeds in the genus Laurencia may be classified into four lineages according to the stereochemical features of their metabolites, i.e. the known obtusane (like obtusol (+)- 1 ), isoobtusane (like isoobtusol (+)- 2 ) and rogiolane (like rogiolol (−)- 3 ) and — structurally revised and renamed here — cartilagineane chamigrene sesquiterpenes (like cartilagineol 10 ), in a vision that encompasses also biogenetic descendants, like cuparane sesquiterpenes, and fits ideas of historical contingency.