Full multinuclear resonance analysis of 4-amino-1,1,2,2,9,9,10,10-octafluoro[2.2]paracyclophane

The complete assignment of 19F, 1H and 13C NMR spectra for a monosubstituted octafluoro[2.2]paracyclophane derivative is described for the first time. The unambiguous assignments were achieved through the combination of 19F--1H HOESY, 1H COSY and 19F COSY techniques and then further confirmed employing a complementary approach using a Karplus-dependent 3JCF interaction. Interesting aspects of the coupling patterns for various JHH, JHF, JCF and JFF interactions are also discussed.     

Complete 1H and 13C NMR assignments of aurasperone A and fonsecinone A, two bis-naphthopyrones produced by Aspergillus aculeatus

Complete assignments of 1H and 13C NMR chemical shifts of the polyketides aurasperone A and fonsecinone A were made by means of nuclear Overhauser enhancement and heteronuclear NMR correlation experiments. These compounds were isolated for the first time from Aspergillus aculeatus, an endophytic fungus obtained from leaves of Melia azedarach(Meliaceae).     

NMR characterization of new 10-membered-ring macrolactones and dihydrobenzophenazine-5-one, oxidized derivatives of benzo[a]phenazines

Peroxidation of the phenazine of beta-lapachone using m-ClC6H4CO3H-CH2Cl2 furnished a macrolactone with a rigid 10-membered ring, and the corresponding N-oxide, along with a dihydrobenzophenazine-5-one. All of the new compounds were fully characterized by spectroscopic methods, with the unambiguous assignment of the hydrogens and carbon NMR signals for the N-oxide, with the aid of 2-D NMR, mainly COSY, HMQC, HSQC and HMBC. For the other two compounds some signals could not be assigned owing to their own intrinsic features.     

Reactions of organocobaloximes with aryldisulfonyl chlorides

Photochemical reactions of benzyl, heteroaromaticmethyl and allylcobaloximes with aryldisulfonyl chlorides yield symmetrical disulfones. Allyl cobaloximes yield allyldisulfones as the major product whereas bibenzyl is the major product in benzylcobaloximes. A time dependent ¹H NMR studies show that bibenzyl is formed from O-benzyldimethylglyoxime - a predominant product in the initial stage of the reaction.     

Bioorganometallic chemistry: biocatalytic oxidation reactions with biomimetic NAD/NADH co-factors and [Cp*Rh(bpy)H] for selective organic synthesis

The biocatalytic, regioselective hydroxylation of 2-hydroxybiphenyl to the corresponding catechol was accomplished utilizing the monooxygenase 2-hydroxybiphenyl 3-monooxygenase (HbpA). The necessary natural 1,4-dihydronicotinamde adenine dinucleotide (NADH) co-factor for this biocatalytic process was replaced by a biomimetic co-factor, N-benzyl-1,4-dihydronicotinamide, 1b. The interaction between the flavin (FAD) containing HbpA enzyme and the corresponding biomimetic NADH compound, N-benzyl-1,4-dihdronicotinamide, 1b, for hydride transfer, was shown to readily occur. The in situ recycling of the reduced NADH biomimic 1b from 1a was accomplished with [Cp*Rh(bpy)H](Cl); however, productive coupling of this regeneration reaction to the enzymatic hydroxylation reaction was not totally successful, due to a deactivation process concerning the HbpA enzyme peripheral groups; i.e., -SH or -NH₂ possibly reacting with the precatalyst, [Cp*Rh(bpy)(H₂O)](Cl)₂, and thus inhibiting the co-factor regeneration process. The deactivation mechanism was studied, and a promising strategy of derivatizing these peripheral -SH or -NH₂ groups with a polymer containing epoxide was successful in circumventing the undesired interaction between HbpA and the precatalyst. This latter strategy allowed tandem co-factor regeneration using 1a or 2a, [Cp*Rh(bpy)(H₂O)](Cl)₂, and formate ion, in conjunction with the polymer bound, FAD containing HbpA enzyme to provide the catechol product.     

Comparison of Ab Initio MP2/6-311+G(d,p) Predicted Carbon–Hydrogen Bond Distances with Experimentally Determined r 0 (C–H) Distances

Fifty different carbon–hydrogen distances have been predicted from ab initio MP2/6-311+G(d,p) calculations, which range from a short value of 1.0611 Å for HCNO to a long value of 1.1044 Å for H₂CO. The values include those predicted for a series of methyl (CH₃) moieties where the two different C–H distances vary by as much as 0.005 Å. These predicted values are compared to r ₀(C–H) distances obtained from the isolated carbon–hydrogen stretching frequencies, as well as to r ₀ or r _s parameters obtained from microwave data. Except for the very short C–H bonds, the ab initio values from the MP2/6–311+G(d,p) calculations can be used for the carbon–hydrogen distances with error limits of ± 0.003 Å. By utilizing the spectral data from CD₃CClO, it is shown that combination bands in the C–H stretching region could cause problems in the identification of the isolated C–H stretching frequency from the CD₂HCClO isotopomer. The value of the ab initio predicted C–H distances for checking unusually long or short r _s (C–H) or r ₀ values is demonstrated.     

Synthesis and spectroscopic study of hexadecaalkyl-substituted rare-earth diphthalocyanines

New hexadecaalkyl-substituted diphthalocyanine complexes of lanthanides ^RPc₂Ln (R = Et, or Bu; Ln = Lu, Dy, or Eu) were synthesized by three methods: in solution in the presence of 1,8-diazabicyclo[5.4.0]undec-7-ene, in a melt of a mixture of the reagents, and under microwave irradiation. The first of the above-mentioned procedures has an advantage for the preparation of Dy and Eu diphthalocyanines, whereas the melt synthesis is a method of choice for the preparation of Lu complexes. The reaction time decreases in going from the first to the third method. The structures of the complexes were confirmed by mass spectrometry, NMR spectroscopy, and electronic absorption spectroscopy.     

Complete 1H and 13C NMR assignments of two phytosterols from roots of Piper nigrum

Using modern NMR techniques, including DQF-COSY, NOESY, HETCOR and HMBC, the full assignments of all 1H and 13C chemical shifts were made for stigmastane-3,6-dione and stigmast-4-ene-3,6-dione, isolated from the roots of Piper nigrum (Piperaceae). Their stereochemistry was resolved by a combination of 2D NOESY data and analysis of coupling constants. The two compounds were isolated from the genus Piper for the first time.     

Simplified chemical and radiochemical synthesis of 2-arachidonoyl-glycerol, an endogenous ligand of cannabinoid receptors

Endocannabinoids have emerged as a new class of lipid mediators, with manifold roles in the central nervous system and in the periphery. Several studies have identified 2-arachidonoyl-glycerol (2-AG) as a major endogenous agonist of cannabinoid receptors. Here, the chemical synthesis of 2-AG is reported, along with the synthesis of its tritium-labeled derivative. These unlabeled and radiolabeled compounds are suitable tools for unravelling some metabolic routes and biological activities of 2-AG in various cells and tissues.