Chemotaxonomic Profiling Through NMR1.

A metabolite screening of cyanobacteria was performed by nuclear magnetic resonance (NMR) analysis of the soluble material obtained through sequential extraction of the biomass with three different extractive ability solvents (hexane, ethyl acetate, and methanol). Twenty-five strains from the Coimbra Collection of Algae (ACOI) belonging to different orders in the botanical code that represent three subsections of the Stainer-Rippka classification were used. The 1 H NMR spectra of hexane extracts showed that only two strains of Nostoc genus accumulated triacylglycerols. Monogalactosyldiacylglycerols and digalactosyldiacylglycerols were the major components of the ethyl acetate extracts in a mono- to digalactosyldiacylglycerols ratio of 4.5 estimated by integration of the signals at δ 3.99 and 3.94 ppm (sn3 glycerol methylene). Oligosaccharides of sucrose and mycosporine-like amino acids, among other polar metabolites, were detected in the methanolic extracts. Strains of Nostocales order contained heterocyst glycolipids, whereas sulphoquinovosyldiacylglycerols were absent in one of the studied strains (Microchaete tenera ACOI 1451). Phosphathidylglycerol was identified as the major phospholipid in the methanolic extracts together with minor amounts of phosphatidylcholine based on 1 H, 31 P 2D correlation experiments. Chemotaxonomic information could be easily obtained through the analysis of the δ 3.0-0.5 ppm (fatty acid distribution) and δ 1.2-1.1 ppm (terminal methyl groups of the aglycons in heterocyst glycolipids) regions of the 1 H NMR spectra of the ethyl acetate and methanol extracts, respectively.

NMR characterization and evaluation of antibacterial and antiobiofilm activity of organic extracts from stationary phase batch cultures of five marine microalgae (Dunaliella sp., D. salina, Chaetoceros calcitrans, C. gracilis and Tisochrysis lutea).

The chemical composition of five marine microalgae (Dunaliella sp., Dunaliella salina, Chaetoceros calcitrans, Chaetoceros gracilis and Tisochrysis lutea) was investigated through nuclear magnetic resonance (NMR) spectroscopic study of the soluble material obtained by sequential extraction with hexane, ethyl acetate (AcOEt) and methanol of biomass from stationary phase cultures. Hexane extracted the major lipids present in the microalgae during the stationary phase of growth, which correspond to storage lipids. Triacylglycerols (TGs) were the only storage lipids produced by Dunaliella and Chaetoceros. In contrast, T. lutea predominantly stored polyunsaturated long-chain alkenones, with sterols also detected as minor components of the hexane extract. The molecular structure of brassicasterol was determined in T. lutea and the presence of squalene in this sample was also unequivocally detected. Monogalactosyldiacylglycerols (MGDGs) and pigments were concentrated in the AcOEt extracts. C. calcitrans and D. salina constituted an exception due to the high amount of TGs and glycerol produced, respectively, by these two strains. Chlorophylls a and b and ß-carotene were the major pigments synthesized by Dunaliella and chlorophyll a and fucoxanthin were the only pigments detected in Chaetoceros and T. lutea. Information concerning the acyl chains present in TGs and MGDGs as well as the positional distribution of acyl chains on the glycerol moiety was obtained by NMR analysis of hexane and AcOEt extracts, with results consistent with those expected for the genera studied. Fatty acid composition of TGs in the two Dunaliella strains was different, with polyunsaturated acyl chains almost absent in the storage lipids produced by D. salina. Except in C. calcitrans, the polar nature of soluble compounds was inferred through the relative extraction yield using methanol as the extraction solvent. Glycerol was the major component of this fraction for the Dunaliella strains. In T. lutea 1,4/2,5-cyclohexanetetrol (CHT) and dimethylsulfoniopropionate (DMSP) preponderated. CHT was also the major polyol present in the Chaetoceros strains in which DMSP was not detected, but prominent signals of 2,3-dihydroxypropane-1-sulfonate (DHSP) were observed in the 1H NMR spectra of methanolic extracts. The presence of DHSP confirms the production of this metabolite by diatoms. In addition, several other minor compounds (digalactosyldiacyglycerols (DGDGs), sulphoquinovosyldiacylglycerols (SQDGs), amino acids, carbohydrates, scyllo-inositol, mannitol, lactic acid and homarine) were also identified in the methanolic extracts. The antibacterial and antibiofilm activities of the extracts were tested. The AcOEt extract from C. gracilis showed a moderate antibiofilm activity.

Synthesis and structure of tridentate bis(phosphinic amide)-phosphine oxide complexes of yttrium nitrate. Applications of 31P,89Y NMR methods in structural elucidation in solution.

The synthesis and characterisation of a tridentate ligand containing two diphenylphosphinic amide side-arms connected through the ortho position to a phenylphosphine oxide moiety and the 1:1 and 2:1 complexes formed with yttrium nitrate are reported for the first time. The free ligand (R(P1)*,S(P3)*)-11 is obtained diastereoselectively by reaction of ortho-lithiated N,N-diisopropyl-P,P-diphenylphosphinic amide with phenylphosphonic dichloride. Complexes [Y((R(P1)*,S(P3)*)-11)(NO(3))(3)] and [Y((R(P1)*,S(P3)*)-11)(2)(NO(3))](NO(3))(2) were isolated by mixing ligand 11 with Y(NO(3))(3)·6H(2)O in acetonitrile at room temperature in a ligand to metal molar ratio of 1:1 and 2:1, respectively. The 1:1 derivative is the product of thermodynamic control when a molar ratio of ligand to yttrium salt of 1:1 is used. The new compounds have been characterised both as the solid (X-ray diffraction) and in solution (multinuclear magnetic resonance). In both yttrium complexes the ligand acts as a tridentate chelate. The arrangement of the two ligands in the 2:1 complex affords a pseudo-meso structure. Tridentate chelation of yttrium(III) in both complexes is retained in solution as evidenced by (89)Y NMR data obtained via(31)P,(89)Y-HMQC, and (89)Y,(31)P-DEPT experiments. The investigation of the solution behaviour of the Y(III) complexes through PGSE NMR diffusion measurements showed that average structures in agreement with the 1:1 and 1:2 stoichiometries are retained in acetonitrile.

Solution and computed structure of O-lithium N,N-diisopropyl-P,P-diphenylphosphinic amide. Unprecedented Li-O-Li-O self-assembly of an aryllithium.

The structural characterization of an ortho-lithiated diphenylphosphinic amide is described for the first time. Multinuclear magnetic resonance ((1)H, (7)Li, (13)C, (31)P) studies as a function of temperature and concentration employing 1D and 2D methods showed that the anion exists as a mixture of one monomer and two diastereomeric dimers. In the dimers the chiral monomer units are assembled in a like and unlike manner through oxygen-lithium bonds, leading to fluxional ladder structures. This self-assembling mode leads to the formation of Li(2)O(2) four-membered rings, a structural motif unprecedented in aryllithium compounds. DFT computations of representative model compounds of ortho-lithiated phosphinic amide monomer and Li(2)C(2) and Li(2)O(2) dimers with different degrees of solvation by THF molecules showed that Li(2)O(2) dimers are thermodynamically favored with respect to the alternative Li(2)C(2) structures by 4.3 kcal mol(-1) in solvent-free species and by 2.3 kcal mol(-1) when each lithium atom is coordinated to one THF molecule. Topological analysis of the electron density distribution revealed that the Li(2)O(2) four-membered ring is characterized by four carbon-lithium bond paths and one oxygen-oxygen bond path. The latter divides the Li-O-Li-O ring into two Li-O-Li three-sided rings, giving rise to two ring critical points. On the contrary, the bond path network in the Li(2)C(2) core includes a catastrophe point, suggesting that this molecular system can be envisaged as an intermediate in the formation of Li(2)O(2) dimers. The computed (13)C chemical shifts of the C-Li carbons support the existence of monomeric and dimeric species containing only one C-Li bond and are consistent with the existence of tricoordinated lithium atoms in all species in solution.

Solution NMR structural study of a mixed aggregate of N-lithium triphenylphosphazene and lithium bromide.

The toluene solution structure of an N-lithio(triphenyl)phosphazene (Ph(3)PNLi) mixed aggregate with lithium bromide (LiBr), 5, has been elucidated for the first time based on multinuclear magnetic resonance measurements ((1)H, (6)Li, (7)Li, (13)C and (31)P). The structure consist of two dimers [Li(mu-Z)](2) (Z= Br, NPR(3)) linked through LiX (X= N, Br) bridges. This arrangement is a cubane-like structure analogous to that found in the solid-state.

Phosphinamide-directed benzylic lithiation. Application to the synthesis of peptide building blocks.

N-benzyldiphenylphosphinamides are deprotonated at the NCalpha position diastereospecifically upon treatment with t-BuLi in diethyl ether at low temperature. The reaction of the anions with alkyl, acyl, and tin halides, aliphatic and aromatic aldehydes, and Michael acceptors allowed installation of a variety of functional groups into the benzylic arm in excellent yields. Cleavage of the P-N linkage affords 1,2-amino alcohols and alpha-, beta-, and gamma-amino acids.

C(alpha),C(ortho)-Dimetalated phosphazene complexes.

The first C(alpha),C(ortho) dilithium complex of a phosphazene has been synthesized as a single stereoisomer and has been structurally characterized in solution; the complex is monomeric, with the dianion acting as an N-C(ortho) and O-C(alpha) chelate. Transmetallation with Me(3)SnCl and PhHgCl afforded the first C(alpha),C(ortho) homo- and hetero-bimetallic phosphazene complexes, which contain a desymmetrised Ph(2)PN moiety.

Unprecedented asymmetric induction through configurationally stable lithium N-(alpha-methylbenzyl)phosphinamides. A new entry to enantiomerically pure gamma-aminophosphinic acids and esters.

The first examples of configurationally stable N-benzyl-N-phosphinoyl carbanions are described. Their applications to the synthesis of homochiral gamma-aminophosphinic acids and esters via highly enantioselective dearomatising reactions are shown.

Conformational mobility of thianthrene-5-oxide.

[reaction: see text] Data on the apparent dipole moment of thianthrene-5-oxide (1) and (1)H NMR spectra in different solvents support the conformational mobility of 1, which flaps between two limit boat conformations with the sulfinyl group in pseudoequatorial and pseudoaxial positions, respectively. The conformational equilibrium of 1 occurs too fast for the (1)H NMR (500 MHz) time-scale even at -130 degrees C, and the equilibrium constant has not been determined. The apparent dipole moments of 1 in n-hexane and 1,4-dioxane and the (1)H NMR spectra of 1 and the model compounds cis- and trans-thianthrene-5,10-dioxides (2) and thianthrene (5) in different solvents and at various temperatures confirm that the relative position of the conformational equilibrium of 1 is solvent-dependent, and more polar solvents favor the conformation with the sulfoxide group in the pseudoaxial position (1(')(ax)). Variable-temperature (1)H NMR spectra have established the interconversion barrier of trans-2 and confirmed that the conformational equilibrium of cis-2 is strongly displaced toward the conformation with both sulfinyl groups in the pseudoequatorial position. The (1)H NMR data support the transannular interaction of the functional groups in 1 and trans-2.

Mechanism of the oxidation of sulfides by dioxiranes: conformational mobility and transannular interaction in the oxidation of thianthrene 5-oxide.

The detailed study of the oxidation of thianthrene 5-oxide (1) with methyl(trifluoromethyl)dioxirane (5b) in different solvents and in the presence of (18)O isotopic tracers is reported. Thianthrene 5-oxide (1) is a flexible molecule in solution, and this property allows for transannular interaction of the sulfoxide group with the expected zwitterionic 7 and hypervalent 10-S-4 sulfurane 9 intermediates formed in the oxidation and biases the course of the reaction toward the monooxygenation pathway.

Regio- and diastereoselective preparation of tetrahydrobenzo[c]-1-aza-2lambda(5)-phospholes through dearomatization cyclization of lithiated N-benzyl-N-alkyl(diphenyl)phosphinamides. Synthesis of gamma-(N-alkylamino)phosphinic acids.

A study of the protonation of the cycloadducts derived from the dearomatization reaction of lithiated N-alkyl-N-benzyldiphenylphosphinamides has been carried out. The regio- and stereoselectivity of the process has been analyzed in terms of the size of the N-alkyl substituent, the acidity and size of the protonating reagent, and the cosolvent used. The optimization of these variables allowed the preparation of tetrahydrobenzo[c]-1-aza-2lambda(5)-phospholes containing a 1,3-cyclohexadiene or 1,4-cyclohexadiene system with moderate to excellent regio- and stereocontrol. The heterocycles were readily hydrolyzed, affording gamma-(N-alkylamino)diphenylphosphinic acids with the functionalities linked to a cyclohexadiene substructure.