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The ground state energies and structures of octamers of poly(methyl)iminomethylene are investigated ab initio at the 6-31G* SCF and MP2 levels and compared with those produced by molecular mechanics (MM), using Allinger's MM3 force field. The torsional parameters used in MM3 calculations for the dihedral angle NCCN (φ) have been obtained from ab initio calculations of model diimines ((E,E), (E,Z), and (Z,Z) N,N‘-diisopropylethanediimine], in the flexible rotor approximation. At the MM level, bulkier substituents have been considered as well (R = isopropyl, 1-cyclohexylethyl). Both at the ab initio and classical level, conformations close to a 41 helix are found to be stable, but they never are the absolute minimum. The minimum energy geometry shows a regularly alternating disposition of the substituents on the iminic double bonds (syndio configuration):  its backbone conformation (dihedral angles φ) shows dimeric sections which are alternatively trans-planar (E,E sections) and close to ±90° (Z,Z sections). The energy gap between the syndio geometry and the 41 helix amounts to ∼30 kcal/mol in the methyl oligomer at the ab initio level vs ∼11 kcal/mol at the MM3 level. This latter value does not change significantly passing from methyl to isopropyl and 1-cyclohexylethyl. Also, conformations having an inversion of the helical sense along the chain (wormlike chains) are found to be stable according to both calculation methods, and their energies are comparable to those of helical conformers. CD calculations were carried out employing an independent systems approach. The calculated intensities of the CD bands of a model 41 helix are much higher than what experimentally found, while those calculated for the syndio structure (considered as composed of a series of diiminic units) are comparable to experiment. A negative CD band is predicted to be associated with the n−π* transition of the iminic chromophore in a 41 P-helix, as previously found in the literature. The preference for nonhelical conformers could account for various features observed in the UV, CD, and NMR spectra of some poly(iminomethylenes), as reported in literature (absorption at long wavelengths, low intensity of CD bands, chemical shift dispersion of backbone carbons resonances).

In addition to the known bioactive triterpene cucurbitacin B (1), two new cucurbitane triterpenoids, namely, leucopaxillones A (3) and B (4), exhibiting a new oxygenation pattern among cucurbitacins, have been isolated from the mushroom Leucopaxillus gentianeus (syn. L. amarus). Cucurbitacin B (1) imparts a bitter taste to the flesh of the fungus; however, it occurs in the fruiting bodies mainly esterified as tasteless fatty acid esters 2a-c. In vitro growth inhibitory effects of compounds 1-4 on proliferation of four different human tumor cell lines (A549, CAKI-1, HepG2, MCF-7) were evaluated by using a 1-day MTT assay. Only cucurbitacin B was highly active on all lines. Free cucurbitacin B is presumed to be formed in vivo by an enzyme-mediated scission of esters 2a-c, thus constituting a chemical weapon that protects the mushrooms against parasites and predators. Compounds 1-4 are structurally different from the other few cucurbitacins isolated from Basidiomycetes, being, instead, more similar to those occurring in plants. In particular, cucurbitacin B (1) seems to represent an interesting example of secondary metabolite convergence between distant taxa such as fungi and vascular plants, where they likely exert a similar role of protection. The structures of the compounds were established by means of spectroscopic methods and X-ray diffraction on a single crystal. The absolute configuration of leucopaxillone A has been assigned on the basis of CD chirality rules.

Seagrasses are high plants sharing adaptive metabolic features with both terrestrial plants and marine algae, resulting in a phytocomplex possibly endowed with interesting biological properties. The aim of this study is to evaluate the in vitro activities on skin cells of an ethanolic extract obtained from the leaves of Posidonia oceanica (L.) Delile, family Potamogetonaceae, herein named Posidonia ethanolic extract (PEE). PEE showed high radical scavenging activity, high phenolic content, and resulted rich in chicoric acid, as determined through HPLC-MS analysis. The use of MTT assay on fibroblasts showed a PEE cytotoxicity threshold (IC05) of 50 µg/mL at 48 h, while a sub-toxic dose of 20 µg/mL induced a significant increase of fibroblast growth rate after 10 days. In addition, an ELISA assay revealed that PEE doses of 5 and 10 µg/mL induced collagen production in fibroblasts. PEE induced dose-dependent mushroom tyrosinase inhibition, up to about 45% inhibition at 1000 µg/mL, while 50% reduction of melanin was observed in melanoma cells exposed to 50 µg/mL PEE. Finally, PEE lipolytic activity was assessed by measuring glycerol release from adipocytes following triglyceride degradation. In conclusion, we have collected new data about the biological activities of the phytocomplex of P. oceanica seagrass on skin cells. Our findings indicate that PEE could be profitably used in the development of products for skin aging, undesired hyperpigmentation, and cellulite.