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Three series of thiophene-based pi-conjugated oligomers built with different combinations of thiophene cycles and double bonds have been synthesized and characterized. The analysis of the chain length dependence of the electronic, electrochemical, and vibrational properties of the three series of oligomers has been carried out using cyclic voltammetry, UV-vis, IR, and Raman spectroscopies. These various investigations provide consistent results showing that incorporation of ethylenic linkages in an oligothiophene structure leads to a faster decrease of the HOMO-LUMO gap with chain extension due to the combined effects of enhanced planarity and lower overall aromatic character of the system. Although the incorporation of two consecutive double bonds in the system leads to a stabilization of the dicationic state, this structural modification does not produce the expected further decrease of the HOMO-LUMO gap at large chain extension. This phenomenon is discussed on the basis of an interplay between aromaticity and bond length alternation.

Crown-annelated quater- (4T) and sexithiophenes (6T) with oligooxyethylene chains of various lengths attached at the 3-positions of the terminal thiophene rings have been synthesized. Analysis of the cation-binding properties of the macrocycles by (1)H NMR and UV-vis spectroscopy reveals the formation of a 1:1 complex with Ba(2+), Sr(2+), or Pb(2+) and shows that cation complexation results in a conformational transition in the pi-conjugated system. Theoretical analysis of this process by density functional methods predicts that this conformational transition results in a narrowing of the highest occupied-lowest unoccupied molecular orbital gap of the conjugated system with a decrease of the redox potentials (E(0)(1) and E(0)(2)) associated with the formation of the 4T cation radical and dication. Cyclic voltammetry shows that, depending on the binding constant, the presence of metal cation produces a negative or a positive shift of E(0)(1) while E(0)(2) always shifts negatively. This unusual behavior is discussed in terms of interplay between electrostatic interactions and conformational changes associated with cation binding.

Eight new 4-phenylfuranocoumarins (1-8) have been isolated from the stem bark and the fruits of Calophyllum dispar, together with three known coumarins. The structures of 1-8 were established by means of spectroscopic analysis, including extensive 2D NMR studies. Some of these furanocoumarins exhibited significant cytotoxic activity against KB cells.

Four new xanthones, caledonixanthones A-D (1-4), were isolated from the trunk bark of Calophyllum caledonicum, in addition to 17 known compounds. The structures of 1-4 were determined by means of spectroscopic analysis and chemical derivatization.

The analogue of zeatin bearing a vinylic fluorine atom and its geometrical isomer were synthesized. The fluorine atom exerts a favorable influence on cytokinin activity in the fluoro analogue of cis-zeatin, but not in the fluoro analogue of zeatin itself. Another series of zeatin derivatives in which the methyl group was replaced by alkyl (ethyl, propyl, and isopropyl), phenyl, and benzyl groups were also obtained. The ethyl analogue was found to be more active than zeatin, while the others were inactive or slightly active. Keywords: Cytokinins; fluoro compounds; synthesis; biological activity

Thienylenevinylene oligomers (nTVs) containing up to 10 thiophene rings and bearing solubilizing hexyl groups at the α-position of the end thiophene rings or octyl or dibutyl chains at the 3-position or the 3- and 4-positions of the thiophene rings have been synthesized by a combination of formylation reaction, Wittig−Horner olefination, and McMurry dimerization. Owing to the good solubility imparted by alkyl chains, the electrochemical behavior of nTVs has been analyzed for the first time. Chain extension leads to a negative shift of the peak potentials corresponding to the formation of the cation radical and dication and to a decrease of their difference. For the octamers the dication is formed directly through a two-electron transfer while the system can be reversibly charged up to the tetracationic state. Electronic absorption spectra show the expected bathochromic shift of λmax and decrease of the HOMO−LUMO gap with extension of the conjugation length. Thus, solution-cast films of octamers exhibit ba...

From the EtOH extract of the stem bark of Mitrella kentii (Annonaceae), two new terpenylated dihydrochalcones were isolated, namely (−)-neolinderatin (1) and (−)-linderatin (2), together with known compounds 2‘,6‘-dihydroxy-4‘-methoxydihydrochalcone and (+)-catechin. Their structures were elucidated by means of combined analytical methods including HREIMS, DC, 1D, and 2D NMR spectroscopies.

A photodynamic molecular architecture has been synthesized by covalent fixation of a photoisomerizable azobenzene group at two fixed points of a conformationally flexible pi-conjugated quaterthiophene chain. The crystallographic structure shows that the two systems lie in parallel planes with a short interplane distance. Theoretical modelization and experimental analysis by 1H NMR and cyclic voltammetry unequivocally show that trans to cis photoisomerization of the azobenzene group induces dimensional and conformational changes in the underlying pi-conjugated system. These geometrical changes produce, in turn, an increase of the HOMO level and a narrowing of the HOMO-LUMO gap, thus providing a first example of photomechanical control of the electronic properties of the pi-conjugated system.

The crinine-type alkaloids (+)-buphanisine and (−)-siculine have been obtained from Sternbergia sicula, while (−)-epimaritinamine and (−)-maritinamine were found in Sternbergia lutea

(−)-Siculinine was obtained from Turkish Sternbergia sicula. (−)-deacetyllutessine is shown to be identical with (−)-ungiminorine

Aristolochia elegans of Egyptian origin has yielded the new bisbenzylisoquinoline (―)-temuconine, which is enantiomeric with the previously described (+)-temuconine obtained from Chilean Berberis valdiviana