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PubMed2005

The gas-phase dipeptide analogue acetyl-phenylalanyl-amide: a model for the study of side chain/backbone interactions in proteins.

The issue of the influence of the side chain/backbone interaction on the local conformational preferences of a phenylalanine residue in a peptide chain is addressed. A synergetic approach is used, which combines gas-phase UV spectroscopy as well as gas-phase IR/UV double-resonance experiments with DFT and post Hartree-Fock calculations. N-Acetyl-Phe-amide was chosen as a model system for which three different conformers were observed. The most stable conformer has been identified as an extended beta(L) conformation of the peptide backbone. It is stabilized by a weak but significant NH-pi interaction bridging the aromatic ring on the residue (i) with the NH group on residue (i+1), with the aromatic side chain being in an anti conformation. This stable conformation corresponds to the common NH(i+1)-aromatic(i) interaction encountered in proteins for the three aromatic residues (phenylalanine, tyrosine, and tryptophan), which illustrates the relevance of gas-phase investigations to structural biology issues. The two other less abundant conformers have been assigned to two gamma-folded backbone conformations that differ by the orientation of the side chain. In all cases, the IR data provided spectroscopic fingerprints of these interactions. Finally, the strong conformational dependence of the fluorescence yield found for N-acetyl-Phe-amide illustrates the role of the environment on the excited-state dynamics of these species, which is often exploited by biochemists to monitor protein structural changes from tryptophan lifetime measurements.

Dipeptides↗
PubMed2005

Ultrafast photoinduced intramolecular charge separation and recombination processes in the oligothiophene-substituted benzene dyads with an amide spacer.

Photoinduced intramolecular charge separation (CS) and recombination (CR) processes of the tetrathiophene-substituted benzene dyads with an amide spacer (4T-PhR, R = 4-H (1), 4-CN (2), 3,4-(CN)2 (3), 4-NO2 (4), 3,5-(NO2)2 (5)) in solvents of different polarities were investigated using various fast spectroscopies. It was revealed that the CS rates depend on the ability of the acceptor and solvent polarity. Ultrafast CS with the rate of 5 x 10(12) s(-1) was revealed for 5 in PhCN and MeCN. The ultrafast CS can be attributed to the large electronic coupling matrix element between the donor and the acceptor despite the relative long donor-acceptor distance. The existence of the state with large electron density on the spacer between 14T*-PhR and LUMO should facilitate the CS process in the present dyad system. It was also revealed that the CR rates in these dyads were rather fast because of the enhanced superexchange interaction through the amide spacer.

Journal Article↗
PubMed2006

Solvation of yttrium with ammonia revisited. Di-amide formation in the reaction of yttrium with ammonia.

The reactivity of yttrium atoms toward ammonia is revisited using expanded density functional theory calculations. The new results reveal that absorption of NH3 on YNH is dissociative to form Y(NH2)2. The di-amide species can adsorb further NH3 molecules molecularly to form Y(NH2)2NH3 and Y(NH2)2(NH3)2. The calculations aimed to reveal the detail of the potential energy curves between the imide and the di-amide forms. The Y(NH2)2(NH3)x species are more stable than those of YNH(NH3)x by more than 20 kcal/mol.

Journal Article↗
PubMed2006

Enhancement of lithium amide to lithium imide transition via mechanical activation.

The decomposition of lithium amide (LiNH2) to lithium imide (Li2NH) and ammonia (NH3) with and without high-energy ball milling is investigated to lay a foundation for identifying methods to enhance the hydrogen uptake/release of the lithium amide and lithium hydride mixture. A wide range of analytical instruments are utilized to provide unambiguous evidence of the effect of mechanical activation. It is shown that ball milling reduces the onset temperature for the decomposition of LiNH2 from 120 degrees C to room temperature. The enhanced decomposition via ball milling is attributed to mechanical activation related to the formation of nanocrystallites, the reduced particle size, the increased surface area, and the decreased activation energy. The more mechanical activation there is, then the more improvement there is in enhancing the decomposition of LiNH2. It also is found that the activation energy for the decomposition of LiNH2 without ball milling is 243.98 kJ/mol, which is reduced to 222.20 kJ/mol after ball milling at room temperature for 45 min and is further reduced to 138.05 kJ/mol after ball milling for 180 min. The rate of the isothermal decomposition at the later phase of the LiNH2 decomposition is controlled by diffusion of NH3 through the Li2NH layer.

Journal Article↗
PubMed2005

Photoinduced gelation by stilbene oxalyl amide compounds.

Oxalyl amide derivatives bearing 4-dodecyloxy-stilbene as a cis-trans photoisomerizing unit were synthesized. The trans derivative acted as a versatile gelator of various organic solvents, whereas the corresponding cis derivative showed a poor gelation ability or none at all. In diluted solution (c = 2.0 x10(-5) mol dm(-3), ethanol), the cis isomer was photochemically converted into the trans isomer within 4 min. Depending on the radiation wavelength, the trans isomer was stable or liable to photodecomposition. When exposed to irradiation, a concentrated solution of the cis isomer (c = 2.0 x 10(-2) mol dm(-3), ethanol) turned into a gel. The FT-Raman, FT-IR, and 1H NMR spectra demonstrated that the gelation process occurred because of a rapid cis --> trans photoisomerization followed by a self-assembly of the trans molecules. Apart from the formation of hydrogen bonding between the oxalyl amide parts of the molecules, confirmed by FT-IR spectroscopy, it was assumed that the pi-pi stacking between the trans-stilbene units of the molecule and a lipophilic interaction between long alkyl chains were the interactions responsible for gelation.

Journal Article↗
PubMed2006

Heterologous biosynthesis of amidated polyketides with novel cyclization regioselectivity from oxytetracycline polyketide synthase.

Heterologous expression of the minimal oxytetracycline polyketide synthase and the amidotransferase OxyD in Streptomyces coelicolor strain CH999 afforded two novel amidated polyketides, WJ85 (4) and WJ85b (5). WJ85 is a C-9 unreduced decaketide that is primed by a malonamyl starter unit. WJ85 is cyclized via an unusual C-11 to C-16 intramolecular aldol condensation not observed among known aromatic polyketides. The structures of WJ85 and the previously characterized WJ35 suggest that the presence of an amide starter unit has a profound effect on the cyclization regioselectivity and reactivity of a polyketide backbone. WJ85b is an anthraquinone and is an oxidized product of WJ85.

Cyclization↗
PubMed1998

Antifungal amide from leaves of Piper hispidum.

Bioactivity-guided fractionation of a CH2Cl2 extract from leaves of Piper hispidum (Piperaceae) yielded a new pyrrolidine amide, N-[7-(3',4'-methylenedioxyphenyl)-2(Z),4(Z)-heptadienoyl] pyrrolidine 1, in addition to two known amides N-[5-(3', 4'-methylenedioxyphenyl)-2(E)-pentadienoyl] pyrrolidine and N-[2-(3', 4'-methylenedioxy-6'-methoxyphenyl)-2(Z)-propenoyl]pyrrolidine. The structure of compound 1 was elucidated by interpretation of spectral data, including ES-MS. Compound 1 showed antifungal activity against Cladosporium sphaerospermum.

Antifungal Agents↗
PubMed1999

A new amide from zanthoxylum armatum

A new amide designated as armatamide (1)-along with two lignans, asarinin and fargesin, alpha- and beta-amyrins, lupeol, and beta-sitosterol-beta-D-glucoside-has been isolated from the bark of Zanthoxylum armatum. The structure of the new compound was deduced by spectral and chemical analysis as N-(4'-methoxyphenyl ethyl)-3, 4-methylenedioxy cinnamoyl amide.

Journal Article↗
PubMed1999

Tryptamine derived amides and acetogenins from the seeds of Rollinia mucosa.

Bioactivity-directed fractionation of a CHCl(3)-MeOH (1:1) extract prepared from the seeds of Rollinia mucosa led to the isolation of a mixture of eight novel tryptamine amides. Extensive HPLC allowed the isolation of the major component of the mixture, which was characterized as N-lignoceroyltryptamine (6) using a combination of spectroscopic and chemical methods. The minor amides were identified by GC-MS analysis as N-palmitoyltryptamine (1), N-stearoyltryptamine (2), N-arachidoyltryptamine (3), N-behenoyltryptamine (4), N-tricosanoyltryptamine (5), N-pentacosanoyltryptamine (7), and N-cerotoyltryptamine (8). Two lignans (pinoresinol dimethyl ether and magnolin) and six acetogenins [membranacin (9), desacetyluvaricin (10), rolliniastatin 1, bullatacin, squamocin, and motrilin] were also isolated. The cytotoxicity of membranacin (9) and desacetyluvaricin (10) against six human solid tumor cell lines was determined. The absolute configuration of the former is reported.

Antineoplastic Agents, Phytogenic↗
PubMed2001

Twisted amides: synthesis and structure of 1,6-dipivaloyl-3,4,7,8- tetramethyl-2,5-dithioglycoluril.

[structure: see text] The 1,6-dipivaloyl derivative of 3,4,7,8-tetramethyl-2,5-dithioglycoluril (6) was prepared and the crystal structure determined by X-ray diffraction; 6 is a twisted amide in which severe ring strain and nonbonded interactions compel both pivaloyl groups to twist dramatically out of the ring plane. The amide oxygen atoms point in opposite directions with respect to the mean plane through the glycoluril core, and the bridgehead methyl groups are forced out of the symmetric syn geometry (eta = 30.5 degrees ). The structure of 7, a rearrangement product generated during synthesis of 6, was also determined by single-crystal X-ray diffraction.

Journal Article↗
PubMed2002

Conversion of N-aromatic amides to O-aromatic esters.

[reaction: see text] N-Aromatic secondary amides can be transformed into O-aromatic esters in high yield via N-nitrosamide intermediates. The amides can be generated in situ from the corresponding aromatic amines or nitro compounds, and phenols can easily be made from the esters. The reaction can be modified by addition of methyl methacrylate or toluene at 0 degrees C to give polymerization or deamination, respectively. The rearrangement mechanism may involve radical formation and recombination.

Journal Article↗
PubMed2003

Lanthanide triflate-promoted palladium-catalyzed cyclization of alkenyl beta-keto esters and amides.

[reaction: see text] Lanthanide triflates were found to promote the palladium-catalyzed cyclization of alkenyl beta-keto esters and amides. In the presence of catalytic amounts of PdCl(2)(MeCN)(2) and Ln(OTf)(3), various alkenyl beta-keto esters and amides underwent regioselective cyclization reactions to give six-, seven-, or eight-membered-ring carbocycles in moderate to excellent yields.

Journal Article↗
PubMed2004

Efficient synthesis of acylsilanes using morpholine amides.

[reaction: see text] A general synthesis of acylsilanes from the corresponding morpholine amides and silyllithium species is described. The use of morpholine amides is economical and prevents over-addition by the silyl nucleophile. The procedure cleanly affords acylsilanes in good yields and circumvents the use of stoichiometric copper(I) cyanide typically employed to synthesize these compounds from acid chlorides.

Journal Article↗
PubMed2004

A new synthesis of naphthyridinones and quinolinones: palladium-catalyzed amidation of o-carbonyl-substituted aryl halides.

[reaction: see text] An alternative to the Friedlander condensation for the synthesis of naphthyridinones and quinolinones has been discovered. Palladium-catalyzed amidation of halo aromatics substituted in the ortho position by a carbonyl functional group or its equivalent with primary or secondary amides leads to the formation of substituted naphthyridinones and quinolinones.

Journal Article↗
PubMed2004

Copper sulfate-pentahydrate-1,10-phenanthroline catalyzed amidations of alkynyl bromides. Synthesis of heteroaromatic amine substituted ynamides.

A practical cross-coupling of amides with alkynyl bromides using catalytic CuSO(4).5H(2)O and 1,10-phenanthroline is described here. This catalytic protocol is more environmentally friendly than the use of CuCN or copper halides and provides a general entry for syntheses of ynamides including various new sulfonyl and heteroaromatic amine substituted ynamides. Given the interest in ynamides, this N-alkynylation of amides should be significant for the future of ynamides in organic synthesis.

Journal Article↗
PubMed2005

Synthesis of C3-symmetric tris(beta-hydroxy amide) ligands and their Ti(IV) complex-catalyzed enantioselective alkynylation of aldehydes.

[reaction: see text]. A series of new chiral C3-symmetric tris(beta-hydroxy amide) ligands have been synthesized via the reaction of 1,3,5-benzenetricarboxylic chloride and optically pure amino alcohols (up to 96% yield). The asymmetric catalytic alkynylation of aldehydes with these new C3-symmetric chiral tris(beta-hydroxy amide) ligands and Ti (O(i)'Pr)4 was investigated. Ligand 4c synthesized from (1R,2S)-(-)-2-amino-1,2-diphenylethanol is effective for the enantioselective alkynylation of various aldehydes, and high enantioselectivity was obtained with aromatic aldehydes and alpha,beta-unsaturated aldehyde (up to 92% ee).

Journal Article↗
PubMed2006

4,5,6,7-Tetrachlorobenzo[d][1,3,2]dioxaborol- 2-ol as an effective catalyst for the amide condensation of sterically demanding carboxylic acids.

[reaction: see text] 4,5,6,7-Tetrachlorobenzo[d][1,3,2]dioxaborole (4a) and 4,5,6,7-tetrachlorobenzo[d][1,3,2]dioxaborol-2-ol (4b) are effective catalysts for the dehydrative amide condensation between an equimolar mixture of carboxylic acids and amines. In particular, these catalysts are greatly superior to 3,5-bis(trifluoromethyl)phenylboronic acid (1) for the amide condensation of sterically demanding carboxylic acids. In contrast, 4c, which is prepared from a 1:2 molar mixture of B(OH)(3) and tetrachlorocatechol, is effective as a Lewis acid-assisted Brønsted acid (LBA) catalyst for Ritter reaction.

Journal Article↗

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