Stereochemical assignment of the fungal metabolite xestodecalactone A by total synthesis

The first synthesis of the macrocyclic natural product xestodecalactone A, a metabolite of a sponge-derived fungus, is described. By the use of methyl 5-hydroxyhexanoate in its R- or S-configured form, or as its racemate as the precursors, both enantiomers of xestodecalactone A as well as the racemic compound were obtained. Comparison of these synthetic products with the natural product by circular dichroism (CD) spectroscopy and by HPLC on a chiral phase revealed the natural product to have the (R)-configuration.     

Comparison of large basis set DFT and MP2 calculations in the study of the barrier for internal rotation of 2,3,5,6‐tetrafluoroanisole

The barrier for internal rotation around the ? OCH₃ bond in 2,3,5,6‐tetrafluoroanisole was calculated using the density functional theory (DFT) and second‐order Møller–Plesset (MP2) methods with Pople's basis sets up to 6‐311++G(3df,2p) and Jensen basis sets up to pc‐3. The results are converged only if fairly large basis sets are used (at least 6‐311++G(3df,2pd) or pc‐2). Both the DFT and MP2 potential energy curves show internal structure. Two minima and three maxima are observed on the curves, arising from the interplay between lone‐pair delocalization and changes in the hybridization around the oxygen atom, together with the attraction between the positively polarized hydrogens in the methyl group and the negatively polarized fluorine atom at the ortho position. These critical points are somehow ironed out by the addition of zero‐point and thermal corrections to the energy curves. At this level, the MP2 method can describe reasonably well the previously determined single‐well experimental rotational barrier, 2.7 ± 2.0 kcal/mol at 298 K, while all DFT methods yield a much smaller result. As observed experimentally, the ? OCH₃ group is perpendicular to the aryl ring in the equilibrium structure, although two very close minima with an intermediate hump at 90° are still observable. The theoretical free energy barrier of rotation at the MP2(full)/pc‐2 level is 2.0 ± 1.0 kcal/mol, in reasonable agreement with the experimental determination. © 2006 Wiley Periodicals, Inc. Int J Quantum Chem, 2007     

Application of artificial neural network on mono- and sesquiterpenes compounds determined by headspace solid-phase microextraction-gas chromatography-mass spectrometry for the Piedmont ricotta cheese traceability

Mono- and sesquiterpenes were used for the traceability of a typical Piedmont (Italy) mountain ricotta cheese produced by nine mountain farms. For each farm a sample of ricotta cheese was collected every 7 days during mountain grazing and analysed using headspace solid-phase microextraction-gas chromatography-mass spectrometry (SPME-GC-MS). Obtained results showed the presence of about 20 monoterpenes (above all alpha-pinene, beta-pinene, camphene, p-cymene, beta-myrcene and limonene) and about 15 sesquiterpenes such as alpha-caryophyllene, alpha-copaene and 9-epi-caryophyllene. Despite a wide concentration variability due to the stages of plant development and the pastured area, there are not able differences between the ricotta cheeses analysed so it is possible with the artificial neural network (ANN) technique to distinguish between different mountain farms.     

Hybridnaturstoffe: Synthese cyclischer Hydroxamsäuren der Estra-1,3,5(10)-trien-Reihe

An approach to a new class of cyclic hydroxamic acids is described leading to a formal combination of a benzoxazine subunit related to some natural aglucones occurring in plants with the steroidal skeleton from two members of the estra-1,3,5(10)-triene series. The annelation procedure for a 4-hydroxy-1,4-oxazine moiety to the aromatic A-ring in estrone ( 1 ) and 1-hydroxy-4-methylestra-1,3,5(10)-trien-17-one ( 7 ), used as steroidal precursors, proceeds in four or three steps, respectively (Schemes 1 and 2, resp.). First, a 2-nitro group is introduced regioselectively by a novel nitrosation-oxidation procedure or by conventional nitration (→ nitrophenols 2 and 8 ). Reaction of the phenolic unit of 2 and 8 with methyl bromoacetate or ethyl chlorooxoacetate gives rise to the nitro esters 3 , 4 , 9 , and 10 , which are subjected to reductive cyclization either by means of Zn dust in ammonium chloride solution (for the acetates) or of H₂/Pt(S)/C (for the sensitive oxalates). Hence, the novel cyclic hydroxamic acids 5 , 6, 11 , and 12 of the estra-1,3,5(10)-triene series are obtained.     

A Convenient access to thienyl‐substituted phthalazines

A synthesis of 1‐alkoxy‐ and 1‐amino‐ substituted 4‐(2‐thienyl)‐phthalazines is described from halo‐derivatives of 4‐(2‐thienyl)‐l‐(2H)‐phthalazinone 3.     

Mononuclear and binuclear wirelike ruthenium(II) complexes with oligo-diethynyl-thiophene bridged back-to-back terpyridine ligands: synthesis and electrochemical and photophysical properties

The syntheses, structural features, electrochemical behavior, absorption spectra, and photophysical properties of five mononuclear complexes [(terpy)Ru(terpy-DEDBT(n)-terpy)](2+), RuT(n), and five binuclear complexes [(terpy)Ru(terpy-DEDBT(n)-terpy)Ru(terpy)](4+), RuT(n)Ru, are reported, where n varies from 1 to 5 so that the metal-metal distance is estimated to be 42 A for the largest binuclear complex, RuT(5)Ru (terpy is 2,2':6',2"-terpyridine and DEDBT is 2,5-diethynyl-3,4-dibutylthiophene). The metal-centered oxidation potentials for the mononuclear and binuclear species are slightly more positive than for the reference [Ru(terpy)(2)](2+) complex, owing to the withdrawing nature of the back-to-back terpyridine ligands incorporating the repeat diethynyl-thiophene units. Comparison of the reduction potentials for the mononuclear and binuclear complexes reveals that the reduction steps are localized either at the terpy fragments of the T(n) ligands or at the terpy peripheral ligands. The spectroscopic results (absorption spectra at room temperature, luminescence spectra and lifetimes at room temperature and at 77 K) in acetonitrile solvent are consistent with the establishment of electronic delocalization within the oligomeric diethynyl-thiophene fragments (DEDBT(n)) of the T(n) ligands; however, the results also indicate that the terpy units of these ligands and the DEDBT(n)fragments are not strongly coupled. Both at room temperature and at 77 K, the (3)metal-to-ligand charge-transfer luminescence of RuT(n) and RuT(n)Ru complexes is strongly depressed in the larger species with respect to what happens for n < or = 2 (where the luminescence quantum yield is phi approximately 10(-4)); this is discussed in terms of the possible intervention of triplet levels localized at the oligothiophene DEDBT(n)(fragments.     

Thecis-trans energy difference in bi-1-cyclopro-pen-1-yl and related compounds

Thecis-trans energy difference of bi-1-cyclopropen-1-yl and the fluorosubstituted derivatives are studied byab initio methods in order to establish the stability of the cis andtrans diene isomers.The results of theab initio method STO-3G points toward thetrans bi-1-cyclopropen-1-yl as the most stable isomer (0.2kcal/mol). The energy of the transition state is about 2.5 kcal/mol above that of thetrans isomer. The electronic transitions of the isomers are also reported.Senior Fullbright-Hays Scholar to Uruguay.     

Colorimetric tools for solid-phase organic synthesis

One of the unresolved problems of solid-phase organic synthesis (SPOS) is the availability of general and rapid methods to monitor the transformation of functional groups present in molecules supported on insoluble supports. Color tests, far from providing the ultimate solution, may help in detection (and sometimes in quantification) of different functional groups. In this short review, we have collected most of the methods available and applied in SPOS with an Experimental Section that describes the procedure we have successfully applied to bead analyses in our laboratories.     

Solvent extraction of N-Cyclohexyl-N-Nitrosohydroxylamine (cnha) into some organic solvents and of the Cu(II)-cnha complex into methyl isobutyl ketone

The distribution equilibria of N-cyclohexyl-N-nitrosohydroxylamine (cnha) in the water-chloroform, water-hexane, water-methyl isobutyl ketone (MIBK) and water-isopentyl alcohol systems, and of the Cu(II)-cnha complex in the water-MIBK system have been studied. From the distribution data the dissociation and distribution constants of the reagent have been calculated; their values are pK(a) = 5.55 +/- 0.10; log K(DR) = 2.46 +/- 0.05 (chloroform), 1.76 +/- 0.11 (MIBK), 1.06 +/- 0.07 (hexane) and 1.48 +/- 0.06 (isopentyl alcohol). In the same way the values of the distribution and stability constants of the Cu(II) complex have been obtained; log K(DC) = 3.51; log beta(1) = 7.23 +/- 0.10 and log beta(2) = 12.00 +/- 0.08. For the determination of cnha in the aqueous phase saturated with MIBK, a spectrophotometric method based on the coloured complex formed by the reagent with Fe(III) has been established. Finally, an analytical method for Cu(II) by atomic-absorption spectrometry after its extraction with cnha into MIBK, is proposed. Its detection limit is 4.6 mug l ., its precision +/- 2.1% and its accuracy 97.5%. This method has been applied to the determination of the copper content in the surface water of the Congest River of Catalonia (Spain).