Iridium(I) dimers with bridging N,N′-di-p-tolylformamidine. X-ray molecular structure of Ir2(μ-p-CH3C6H4NCHN-p-C6H4CH3)(μ-NH-p-C6H4CH3)(C8H14)2

The reaction of [IrCl(COD)]₂ with K[CH(N-p- C₆H₄CH₃)₂] (K⁺form⁻) has been carried out in both neat toluene and in the presence of Bu^tOH. In the first case [Ir(form)(COD)]₂ (1) was obtained in good yields. The other reaction follows a somewhat different course with partial alcoholysis of the formamidine ligand and formation of Ir₂(μ-form)(μ-NH-p-C₆H₄CH₃)(COD)₂ (2). Crystal data for compound 2: space group P2₁/c, a = 9.389(2), b = 21.083(4), c = 16.810(2) Å, β = 91.54(1)° V=3326(2) ų, Z = 4, R = 0.0343 for 3707 data with F_o² > 3σ(F_o²).     

Selective synthesis of cerebrosides: (2S, 3R, 4E)-1-O-β-d-galactopyranosyl-N-(2′R and 2′S)-2′-hydroxytetracosanoyl-sphingenine

The cerebrosides were first isolated by Thudicum in 1874 and the structures were established by Carteret al. in 1950 (for review, see [2]). In 1961 Shapiro and Flowers [3] reported the first total synthesis of a cerebroside1 (Fig. 1) which was identified with the natural sample, only through comparison of their i.r. data. In order to confirm the absolute configuration at C-2 of natural cerebroside1, we describe here an unambiguous synthesis of two stereoisomeric cerebrosides1 and2, and found that the¹H-NMR spectra of the synthetic1 (Fig. 2) was completely identical with that of the natural cerebroside reported recently by Dabrowskiet al. [4].In planning the synthetic route, the target structures1 and2 were disconnected at the dotted lines to give three key synthetic intermediates3, 4 and5 or6 (Fig. 1).Abbreviations Bu butyl - Ph phenyl - t-BuPh₂SiCl t-butyldiphenylsilyl chloride - MTPA -methoxy--trifluoromethylphenylacetic acid - THF tetrahydrofuran Part 36 in the series Synthetic Studies on Cell-surface Glycans, for part 35, see [1]     

Total synthesis of cerebrosides: (2S, 3R, 4E)-1-O-β-d-galactopyranosyl-N-(2′R and 2′S)-2′-hydroxytetracosanoylsphingenine

Total syntheses of both (2S, 3R, 4E)-1-O-β-d-galactopyranosyl-N-(2′R)-2′-hydroxytetracosanoylsphingenine 23 and the (2′S) stereoisomer were performed in an unambiguous way by employing either (2S, 3R, 4E)-N-(2′R)-2′-(tert-butyl-diphenylsilyloxy)tetracosanoylsphingenine or its (2′S) stereoisomer as the key glycosyl acceptors. The synthetic cerebroside 23 was shown to be identical with the natural product through comparison of their 400-MHz, ¹H-n.m.r. spectra, thus providing synthetic evidence for the 2′R configuration of the natural cerebroside.     

DFT study on the reactions of ClO–/BrO– with RCl (R = CH3, C2H5, and C3H7) in gas phase

Gas-phase reactions of ClO^–/BrO^– with RCl (R = CH₃, C₂H₅, and C₃H₇) have been investigated in detail using the popular DFT functional BHandHLYP/aug-cc-pVDZ level of theory. As a result, our findings strongly suggest that the type of reaction is firstly initiated by a typical S_N2 fashion. Subsequently, two competitive substitution steps, named as S_N2-induced substitution and S_N2-induced elimination, respectively, would proceed before the initial S_N2 product ion-dipole complex separates, in which the former exhibits less reactivity than the latter. Those are consistent with relevant experimental results. Moreover, we have also explored reactivity difference for the title reactions in term of some factors derived from methyl group, p-π electronic conjugation, ionization energy (IE), as well as molecular orbital (MO) analysis.

Measurement of 2J(H,C)- and 3J(H,C)-coupling constants by α/β selective HC(C)H-TOCSY

A new heteronuclear NMR pulse sequence for the measurement of ⁿJ(C,H) coupling constants, the /selective HC(C)H-TOCSY, is described. It is shown that the S³E element (Meissner et al., 1997a,b) can be used to obtain spin state selective coherence transfer in molecules, in which adjacent CH moieties are labeled with ¹³C. Application of the / selective HC(C)H-TOCSY to a 10nt RNA tetraloop 5-CGCUUUUGCG-3, in which the four uridine residues are ¹³C labeled in the sugar moiety, allowed measurement of two bond and three bond J(C,H) coupling constants, which provide additional restraints to characterize the sugar ring conformation of RNA in cases of conformational averaging.     

Stereoselective Synthesis of (2R, 3S)-2-Benzyl-2-hydroxy-3- (3,4-methylenedioxybenzyl)-γ-butyrolactone from L-(+)-Arabinose

As a model experiment for the stereoselective synthesis of optically active cis-α,β-dibenzyl-α-hydroxy-γ-butyrolactone, (2R, 3S)-2-benzyl-2-hydroxy-3-(3,4-methylenedioxybenzyl)-γ-butyrolactone (3) was stereoselectively synthesized from L-(+)-arabinose.     

Synthesis of new mer,trans-rhodium(III) hydrido-bis(acetylide) complexes: Structure of mer,trans-[(PMe3)3Rh(CC–C6H4-4-NMe2)2H]

Terminal alkynes (R–CC–H, R = 1-naphthyl, 9-anthryl, 4-Me₂N–C₆H₄–, or the longer analogue, 4-(4-Me₂N–C₆H₄–CC–)–C₆H₄–) react with [Rh(PMe₃)₄Me] at ambient temperature, with loss of methane and one PMe₃ ligand, to form the corresponding mer,trans-[(PMe₃)₃Rh(CCR)₂H] compounds in excellent yield. In this preliminary study, the synthesis and spectroscopic characterization of the four new compounds are reported, along with the single-crystal structure of the R = 4-Me₂N–C₆H₄ derivative.     

Antitubercular activity of α,ω-diaminoalkanes,H2N(CH2)nNH2

A series of 11 α,ω-diaminoalkanes, (H₂N(CH₂)_nNH₂, n = 2–12) have been evaluated for their in vitro antibacterial activity against Mycobacterium tuberculosis H37Rv. Compounds, (H₂N(CH₂)_nNH₂, n = 9–12), exhibited a very good activities in the range 2.50–3.12 μg/mL, which can be compared with that of the first line drug, ethambutol (3.12 μg/mL). These results and a preliminary QSAR study can be considered an important start point for the rational design of new leads for anti-TB compounds.     

Influence of ligands on the fac⇌Δhνmer isomerization in [RuCl3(NO)(P–P)] complexes, [P–P = R2P(CH2)nPR2 (n = 1–3) and R2P(CH2)POR2, PR2–CHCH–PR2, R = Ph and (C6H11)2P-(CH2)2-P(C6H11)2]

[RuCl₃(NO)(P–P)], [P–P = R₂P(CH₂)_nPR₂ (n = 1–3) and R₂P(CH₂)POR₂, PR₂–CHCH–PR₂, R = Ph and (C₆H₁₁)₂P-(CH₂)₂-P(C₆H₁₁)₂] were obtained and characterized by ³¹P {¹H} NMR, IR spectroscopies and cyclic voltammetry. The structures of fac-[RuCl₃(NO)(P–P)], P–P = dppm (1), dppe (2), c-dppen (3) and dppp (4), mer-[RuCl₃(NO)(dcpe)] (6a) and mer-[RuCl₃(NO)(dppmO)] (7) have been determined by X-ray diffraction. Photochemical isomerization of fac- to mer-[RuCl₃(NO)(P–P)] was observed under white light in a CH₂Cl₂ solution and in solid state. The isomerization processes were followed by IR and ³¹P {¹H} spectra. The mer-[RuCl₃(¹⁵NO)(dppb)] isomer was used for the definition of the phosphorus atoms in the structure of the complex in solution. The electrochemical study shows that the oxidation/reduction processes observed in these complexes are dependent on both the isomer (fac or mer) and the solvent. In CH₂Cl₂, the NO⁺ reduction potentials are less negative for the mer-isomers than for the fac ones, while in CH₃CN solvent these potentials are, in general, very close for both isomers.     

Crystal Structure of a Tightly Bound Inhibitor of Adenosine Transport N6-(4-Nitrobenzyl)-β-D-2′-Deoxyadenosine Methanol Solvate,C17H18N6O5.1/2 CH3OH

Abstract

The molecular structure of N⁶-(4-nitrobenzyl)-β-D-2′-deoxyadenosine (I) has been determined by single crystal X-ray diffraction. A potent inhibitor of adenosine permeation in cultured S49 mouse lymphoma cells, I binds tightly (K_D 2.4 nM) to high affinity membrane sites present on the nucleoside transporter elements of these cells. Compound I crystallizes in the trigonal space group P3₂21 with unit cell dimensions a = b = 8.0009(9)Å, c = 49.174(8)Å, and Z = 6. The structure was solved by direct methods and refined by least-squares to a final R = 0.038. The mean plane of the 4-nitrobenzyl group, an important substituent for potent nucleoside transport inhibition in a series of S6-substituted 6-thioinosine derivatives, is inclined at an angle of 120.6° to the plane of the adenine ring. The torsion angles around the methylene carbon atom of this benzyl group are C(6)-N(6)-C(10)-C(11), 96.6° and N(6)-C(10)-C(11)-C(12), 93.6°. The glycosidic torsion angle, X, is 217.1° which corresponds to the common anti nucleoside conformation. The deoxyribose ring, however, has the unusual C(1′)-exo conformation, with C(1′) displaced 0.608Å from the plane of C(2′), C(3′), C(4′) and O(4′). The conformation about the exocyclic C(4′)-C(5′) bond is gauche⁺.     

The structure and properties of tetrakis(tironato)cerate(IV), Na12[Ce(C6H2O2(SO3)2)4]·9H2O·6C3H7NO

The title complex, prepared in 1 M NaOH, was crystallized from hot N,N-dimethylformamide/ ethanol solutions to give Na₁₂[Ce(C₆H₂O₂(SO₃)₂)₄]· 9H₂O·6DMF. The purple—brown crystals were examined by X-ray diffraction while inside quartz capillaries filled with DMF, (λ_max 425 nm, ϵ 3664; λ_sh 520 nm, ϵ 2240) and belong to space group Pbca, Z=8 with a=21.846(4), b=17.348(2), c=43.103- (6) Å, V=16.335(7) ų, D_c=1.693 gcm^t−3, D_o=1.725 g cm^t−3. Diffractometer data were collected using Mo Kα radiation to 2θ=43^o. For 7331 independent data with F_o²>3σ(F_o²) full matrix least squares refinement converged to unweighted and weighted R factors of 0.072 and 0.110, respectively, with a mixture of anisotropic and isotropic thermal parameters. The disordered DMF atom parameters were not refined. The structure consists of discrete monomeric Ce(C₆H₂S₂O₈)₄¹²⁻ units with 12 Na⁺ counter cations and 10 H₂O molecules (two with half occupancy), and 6 DMF molecules of solvation filling up spaces between cations and anions. Cerium(IV) is in a general position with a coordination polyhedron close to the trigonal-faced dodecahedron, D_2d, with the angles between the two BAAB trapezoids of 2.3^o and 3.7^o. The average CeO(A) distance, 2.363(9) Å is longer than the average CeO(B) distance, 2.326(15)Å, with the reverse being true for one of the four tironato ligands. The average ring OCeO angle is 67.9(1)^o. The cerium (IV) complex is found by cyclic voltammetry to undergo a quasi-reversible one-electron reduction (in strongly basic solution with excess tiron) with Ef=−497 mV vs. SCE, hence the ratio of the formation constants for tetrakis(tironato)cerate(IV) to that for tetrakis(tironato)cerate(III), K_IV/K_III, is 10³³. Characterization of other tiron salts is reported.     

Asymmetric Hydrolysis of (R,S)-5-Acetoxymethyl-3-tert-butyl-oxazolidin-2-one with Enzymes and Microorganisms†

Enzymes and microorganisms were screened for the asymmetric hydrolysis of (R, S)-5-acetoxymethyl-3-tert-butyl-oxazolidin-2-one 1. Lipases from Pseudomonas aeruginosa and Alcaligenes species, and microorganisms which belong to Enterobacter species or Klebsiella species were found to hydrolyze 1 enantioselectively to give (R)-5-hydroxymethyl-3-tert-butyl-oxazolidin-2-one (R)-2 and (S)-l. (S)-2, one of the typical intermediates for preparing optically active β-blocking agents (β-blockers), was obtained with high enantiomeric excess (91~98% e.e.) from (S)-1.     

Preparation of (±)-2-(2,3-2H2)Jasmonic Acid and Its Methyl Ester,Methyl (±)-2-(2,3-2H2)Jasmonate

For use as the internal standards in a quantitative analysis of natural jasmonic acid (JA) and methyl jasmonate (JAMe) by gas chromatography-mass spectrometry-selected ion monitoring, (±)-2-(2,3–²H₂)JA and its methyl ester, (±)-2-(2,3–²H₂)JAMe, were efficiently prepared from 2-(2–pentyl)-2-cyclopentenone through catalytic semi-deuteriogenation of acetylenic intermediates with deuterium gas in pyridine.     

The luminescence of europium nitrate hexahydrate,Eu(NO3)3·6H2O

Some luminescent properties of single crystals of Eu(NO₃)₃·6H₂O are reported at temperatures down to liquid helium. The water molecules are responsible for a considerable amount of quenching of the emission. The Eu³⁺ coordination changes upon lowering the temperature. The number of ⁵D₀-⁷F₂ lines observed is higher than expected.     

Photobromination of 1,5-Anhydro-2,3-O-isopropylidene-β-d-ribofuranose and Synthesis of (5R) and (5S)-(5-2H1)-d-Riboses

The photobromination of 1,5-anhydro-2,3-O-isopropylidene-β-d-ribofuranose gave the corresponding (5S)-5-bromo compound. The reduction of the bromide with triphenyltindeuteride gave (5S)-(5-²H₁)-1,5-anhydro-2,3-O-isopropylidene-β-d-ribofuranose, with a chiral purity of 76% at C-5, which was converted to (5R)- and (5S)-(5-²H₁)-d-riboses and other ribofuranose derivatives.     

Stereoselective Synthesis of 1- and 2-O-α-d-Cellotriosyl-3-deoxy-2(R)- and 2(S)-glycerols Related to Rhynchosporoside

The stereoselective synthesis of 1- and 2-O-α-d-cellotriosyl-3-deoxy-2(R)- and 2(S)-glycerols, which determined the structure of rhynchosporoside produced by Rhynchosporium secalis, and their phytotoxicity toward the host plant (Hordeum vulgare) are described in detail.