Profiling planktonic biomass using element-specific, multicomponent nuclear magnetic resonance spectroscopy.

Planktonic metabolism plays crucial roles in Earth's elemental cycles. Chemical speciation as well as elemental stoichiometry is important for advancing our understanding of planktonic roles in biogeochemical cycles. In this study, a multicomponent solid-state nuclear magnetic resonance (NMR) approach is proposed for chemical speciation of cellular components, using several advanced NMR techniques. Measurements by ssNMR were performed on (13)C and (15)N-labeled Euglena gracilis, a flagellated protist. 3D dipolar-assisted rotational resonance, double-cross-polarization (1)H-(13)C correlation spectroscopy, and (1)H-(13)C solid-state heteronuclear single quantum correlation spectroscopy successively allowed characterization of cellular components. These techniques were then applied to E. gracilis cultured in high and low ammonium media to demonstrate the power of this method for profiling and comparing cellular components. Cellular NMR spectra indicated that ammonium induced both paramylon degradation and amination. Arginine was stored as a nitrogen reserve and ammonium replaced by arginine catabolism via the arginine dihydrolase pathway. (15)N and (31)P cellular ssNMR indicated arginine and polyphosphate accumulation in E. gracilis, respectively. This chemical speciation technique will contribute to environmental research by providing detailed information on environmental chemical properties.

Radical photocyclization route for macrocyclic lactone ring expansion and conversion to macrocyclic lactams and ketones.

A new method for the synthesis of macrocyclic lactones, lactams, and ketones, which utilizes photoinduced intramolecular radical cyclization reactions of substrates containing tethered carboxylic acids and α,ß-unsaturated carbonyl moieties, has been uncovered. Photocyclization of the carboxylic acids tethered acrylate ester, which were prepared starting from the macrocyclic lactones, gave the two-carbon elongated macrocyclic lactones via decarboxylation. Similar photoreactions of carboxylic acid tethered acryl amide or α,ß-unsaturated ketone moieties, which were also prepared starting from the macrocyclic lactones, produced macrocyclic lactams or ketones, respectively. The simple approach can be readily applied to the preparation of a variety of macrocyclic lactones, lactams, and ketones with tunable ring sizes.

A mild deuterium exchange reaction of free carboxylic acids by photochemical decarboxylation.

Deuterium exchange of a carboxy group was achieved by photochemical decarboxylation of free carboxylic acids in the presence of thiol and a small amount of D(2)O, and a deuterated product with excellent deuterium content was obtained; this reaction is a practical means of synthesizing regioselective deuterium-labelled compounds under mild reaction conditions.

Influence of solvent, electron acceptors and arenes on photochemical decarboxylation of free carboxylic acids via single electron transfer (SET).

Single electron transfer (SET)-photochemical decarboxylation of free carboxylic acids was performed in a polar solvent using several arenes such as phenanthrene, naphthalene, 1-methylnaphthalene, biphenyl, triphenylene, and chrysene in the presence of various electron acceptors such as 1,2-, 1,3-, and 1,4-dicyanobenzenes, methyl 4-cyanobenzoate, and 1,4-dicyanonaphthalene. The decarboxylation reaction was influenced by the arenes, electron acceptors, and solvent. The best result was achieved by the photoreaction using biphenyl and 1,4-dicyanonaphthalene in aqueous acetonitrile.

Enantioselective intramolecular oxidative aminocarbonylation of alkenylureas catalyzed by palladium-spiro bis(isoxazoline) complexes.

An enantioselective synthesis of tetrahydropyrrolo[1,2-c]pyrimidine-1,3-diones via a palladium-catalyzed intramolecular oxidative aminocarbonylation is described. The carbon-carbon double bond of alkenylurea substrates has been shown to react intramolecularly with a nitrogen nucleophile in the presence of a palladium catalyst under a carbon monoxide atmosphere. The use of a chiral spiro bis(isoxazoline) ligand (SPRIX) is essential to obtain the desired products in optically active forms. In comparison with the coordination ability of other known ligands, this peculiar character of SPRIX originates from two structural characteristics: low sigma-donor ability of the isoxazoline coordination site and rigidity of the spiro skeleton.

Inter- and intramolecular addition reactions of electron-deficient alkenes with alkyl radicals, generated by SET-photochemical decarboxylation of carboxylic acids, serve as a mild and efficient method for the preparation of gamma-amino acids and macrocyclic lactones.

Inter- and intramolecular additions of alkyl radicals, generated by SET photochemical decarboxylation reactions of free carboxylic acids, to electron-deficient alkenes take place under mild conditions as part of efficient routes for the formation of N-Boc gamma-amino acids and macrocyclic lactones.

Pd(II)/Pd(IV) catalytic enantioselective synthesis of bicyclo[3.1.0]hexanes via oxidative cyclization of enynes.

The first asymmetric Pd(II)/Pd(IV) catalysis has been achieved by employing the combination of a hypervalent iodine reagent and a chiral ligand, SPRIX. Enantioselective cyclization of enyne derivatives catalyzed by the Pd-i-Pr-SPRIX complex furnished lactones bearing a bicyclo[3.1.0]hexane skeleton with up to 95% ee.

Transformation of ergosterol peroxide to cytotoxic substances by rat intestinal bacteria.

Ergosterol peroxide (EPO, 1) is a major antitumor sterol produced by edible or medicinal mushrooms. Following oral administration of 1 to rats or anaerobic in vitro incubation of 1 with rat fecal bacteria, three metabolites were detected and their structures were identified to be 5alpha,6alpha-epoxyergosta-8(14),22-diene-3beta,7alpha-diol (M1, 2), 5alpha,6alpha-epoxyergosta-8,22-diene-3beta,7alpha-diol (M2, 3), and 5alpha,6alpha-epoxy-3beta-hydroxyergosta-22-ene-7-one (M3, 4) by spectroscopic analysis. Of these, M2 and M3 showed more potent inhibitory activity than the original compound 1 against proliferation of CACO-2, WiDr, DLD-1 and Colo320 human colorectal adenocarcinoma cells. These findings suggest that bacterial metabolites of EPO play a significant role in its cytotoxic activity against human colorectal cancer cells.

Decarboxylative reduction of free aliphatic carboxylic acids by photogenerated cation radical.

The decarboxylation of free carboxylic acids was effected by a photogenerated cation radical of phenanthrene to yield the reduction product in the presence of a thiol, which provides an alternative method to the Barton decarboxylation procedure for aliphatic acids such as N-Boc amino acids.

Crystal structure of Diels-Alder cycloadduct formed from 1-(1,2,3-1H-benzotriazol-1-yl)-2-(4-methylphenyl)-2H-isoindole and dimethyl acetylenedicarboxylate.

The structure of the Diels-Alder cycloadduct formed from 2-(1,2,3-1H-benzotriazol-1-yl)-2-(p-tolyl)-2H-isoindole and dimethyl acetylenedicarboxylate was proved as 11-aza-1-(1,2,3-1H-benzotriazol-1-yl)-11-(4-methylphenyl)-tricyclo-[5.2.1.0(2.7)]undeca-2,4,6.9-tetraene-9,10-dioic acid dimethyl ester. The benzotriazole moiety was located as its 1-yl form, analogous to previous reports. The benzotriazole and the benzene (of tricyclo framework) planes were twisted with an angle of 115.83 degrees. Intramolecular close contacts between benzotriazole and ester are characteristic [N(3)...C(26), 2.754(3)A; N(3)...H(22), 3.26(4)A]. The shortest contact of N(3)...H(22) accounting for the rotation of the methyl group is estimated to be 3.10 A, which might be reasonable as C-H...N-type hydrogen bonding.

Crystal structure of dissymmetrically trihydrated N,N',N''-tribenzoylmelamine (TBM).

In the crystal structure of TBM-trihydrate three waters of crystallization were found to locate dissymmetrically. Thus, one of them forms a chelated ring with the neighboring C=O and N-H of TBM. Two other ones bind each other through hydrogen bonding and two sets of which form a cyclic dimer by hydrogen bonding (namely, water-tetramer). A C=O group binds by hydrogen bonding to each of the tetrameric water. The spatial volume occupied by water-tetramer appears to be sufficient for complexation with organic molecules.

Tryptophan interactions in bacteriorhodopsin: a heteronuclear solid-state NMR study.

The bulky and amphiphilic nature of tryptophan residues makes them particularly interesting components of proteins. In bacteriorhodopsin, four of the eight tryptophan residues are in the active site, forming parts of the retinal binding pocket. In this work, we use solid-state NMR to study the interactions of the tryptophan residues in wild-type bacteriorhodopsin, in the resting state, and in critical intermediates of the proton-motive photocycle. The range of the chemical shifts of the indole nitrogens suggests that all eight of them are hydrogen bonded. Using difference spectroscopy, we isolate several changes in these hydrogen bonds in the early and late M states. As found earlier for the peptide backbone, some perturbations found in the early M state relax in the transition to the late M state while new perturbations arise. Interestingly, Rotational Echo DOuble Resonance (REDOR) difference spectroscopy of [20-13C]retinal,[indole-15N]Trp-bR shows that indole of Trp182 is not involved in the significant hydrogen bond perturbations. We also use REDOR to measure dipolar interactions in [20-13C]retinal,[indole-15N]Trp-bR, and thereby determine the distance between the C20 of retinal and the indole nitrogen of Trp182. The internuclear distance changes only slightly from the light-adapted state (3.36 +/- 0.2 A) to the early M state (3.16 +/- 0.4 A).