Catalytic hydrogenation of tertiary amides at low temperatures and pressures using bimetallic Pt/Re-based catalysts

Hydrogenation of tertiary amides, in particular, N-methylpyrrolidin-2-one, can be efficiently facilitated by a TiO(2)-supported bimetallic Pt/Re catalyst at low temperatures and pressures. Characterisation of the catalysts and kinetic tests have shown that the close interaction between the Re and Pt is crucial to the high activity observed. DFT calculations were used to examine a range of metal combinations and show that the role of the uncoordinated Re is to activate the C=O and that of the Pt is as a hydrogenation catalyst, removing intermediates from the catalyst surface. The rate enhancement observed on the TiO(2) support is thought to be due to the presence of oxygen vacancies allowing adsorption and weakening of the C=O bond. (C) 2011 Elsevier Inc. All rights reserved.

Density Functional Theory Study on the Cleavage Mechanism of the Carbonyl Bond in Amides on Flat and Stepped Ru Surfaces: Hydrogen-Induced or Direct C-O Bond Breaking?

We have performed density functional theory (DFT) calculations to investigate the reaction mechanism of the cleavage of the carbonyl bond in amides on both flat and stepped Ru surfaces. The simplest amide molecule, N,N-dimethylacetamide (DMA), was used as the exemplar model molecule. Through the calculations, the most stable transition states (TSs) in all the pathways on both flat and stepped Ru surfaces are identified. Comparing the energy profiles of different reaction pathways, we find that a direct cleavage mechanism is always energetically favored as compared with an alternative hydrogen-induced mechanism on either the flat or stepped Ru surface. It is easier for the dissociation process to occur on the stepped surface than on the flat surface. However, as compared with the terrace, the superiority of step sites boosting the C-O bond dissociation is not as evident as that on CO dissociation.

Feleucins: Novel Bombinin Precursor-Encoded Nonapeptide Amides from the Skin Secretion of Bombina variegata

The first amphibian skin antimicrobial peptide (AMP) to be identified was named bombinin, reflecting its origin from the skin of the European yellow-bellied toad (Bombina variegata). Bombinins and their related peptides, the bombinin Hs, were subsequently reported from other bombinid toads. Molecular cloning of bombinin-encoding cDNAs from skin found that bombinins and bombinin Hs were coencoded on the same precursor proteins. Here, we report the molecular cloning of two novel cDNAs from a skin secretion-derived cDNA library of B. variegata whose open-reading frames each encode a novel bombinin (GIGGALLNVGKVALKGLAKGLAEHFANamide) and a C-terminally located single copy of a novel nonapeptide (FLGLLGGLLamide or FLGLIGSLLamide). These novel nonapeptides were named feleucin-BV1 and feleucin-BV2, respectively. The novel bombinin exhibited 89% identity to homologues from the toads, B. microdeladigitora and B. maxima. The feleucins exhibited no identity with any amphibian AMP archived in databases. Synthetic feleucins exhibited a weak activity against Staphylococcus aureus (128–256 mg/L) but feleucin-BV1 exhibited a synergistic action with the novel bombinin. The present report clearly demonstrates that the skin secretions of bombinid toads continue to represent a source of peptides of novel structure that could provide templates for the design of therapeutics.

Effect of cultivar and storage time on the volatile flavor components of baked potato

Tubers of five cultivars of potato were stored at 4 degreesC for 2 3 and 8 months and baked in a conventional oven The flavor compounds from the baked potato flesh were isolated by headspace adsorption onto Tenax and analyzed by gas chromatography-mass spectrometry On a quantitative basis compounds derived from lipid and Maillard reaction/sugar degradation dominated the flavor isolates with sulfur compounds, methoxypyrazines, and terpenes making smaller contributions Levels of 37 of the > 150 detected compounds were monitored in each cultivar with time of storage Many significant differences were found in levels of individual compounds compound classes and total monitored compounds for the individual effects of cultivar and storage time and for their two way interaction Differences may be explained by variations in levels of flavor precursors and activities of enzymes mediating flavor compound formation among cultivars and storage times In addition differences in agronomic conditions may partly account for variations among cultivars Overall of the compounds monitored those most likely having the greatest flavor impact were 2-isopropyl 3 methyoxypyrazine 2 isobutyl 3-methoxypyrazine dimethyl trisulfide, decanal and 3 methylbutanal, with methylpropanal, 2 methylbutanal methional, and nonanal also being probable important contributors to flavor.

Volatile flavour components of baked potato flesh. A comparison of eleven potato cultivars

Tubers of eleven cultivars of potato were baked and the flavour compounds from the flesh were isolated by headspace adsorption onto Tenax and analysed by gas chromatography-mass spectrometry (GC-MS). Lipid degradation and the Maillard reaction were the main sources of flavour compounds, accounting for 22-69% and 28-77%, respectively, of the total yields. Various sulfur compounds, methoxypyrazines and terpenes were also identified at lower levels. Relative aroma impact values (RAVs) were calculated by dividing compound yields by the odour threshold value. Compounds contributing most to aroma (RAV > 10000 in at least one cultivar) were 2-isobutyl-3-methoxypyrazine, 2-isopropyl-3-methoxypyrazine, beta -damascenone, dimethyl trisulfide, decanal and 3-methylbutanal. The observed differences in yields and RAVs for compounds among cultivars would be expected to result in differences in perceived flavour.

The carbenoid approach to peptide synthesis

A different approach to the synthesis of dipeptides is described based on the formation of the (NHCHRCONH)-C-1-(CHRCO)-C-2 bond by carbenoid N-H insertion, rather than the formation of the peptide bond itself. Thus decomposition of triethyl diazophosphonoacetate catalysed by rhodium(Ii) acetate in the presence of N-protected amino acid amides 8 gives the phosphonates 9, Subsequent Wadsworth-Emmons reaction of 9 with aldehydes in the presence of DBU gives dehydro dipeptides 10. The reaction has been extended to a simple two-step procedure, without the isolation of the intermediate phosphonate. for conversion of a range of amino acid amides 11 into dehydro dipepides 12 and to an N-methylamide 11h, and for conversion of a dipeptide: to tripeptide (13-14). Direct conversion, by using methyl diazophenylacetate, of amino acid amides to phenylglycine-containing dipeptides 19 proceeds in good chemical yield, but with poor diastereoselectivity.

Transamidation reactions of  -lactams: a synthesis of ( )-dihydroperiphylline.

Ammonolysis of N-(halogenoalkyl)azetidin-2-ones affords medium ring azalactams via transamidation but large or strained rings are not isolated, acyclic ?-amino-amides being produced; two successive transamidative ring expansions from 4-phenylazetidin-2-one give a synthesis of (?)-dihydroperiphylline (I).

N-H insertion reactions of rhodium carbenoids. Part 2. Preparation of N-substituted amino(phosphoryl)acetates (N-substituted phosphorylglycine esters).

Rhodium(II) acetate-catalyzed reaction of Et 2-diazo-2-diethoxyphosphorylate, EtO2CC(:N2)PO(OEt)2, with carbamates, amides, ureas or anilines gives a range of N-substituted 2-amino-2-diethoxyphosphorylacetates, EtO2CCH(NHR1)PO(OEt)2 (where R1 = Boc, Cbz, acetyl, propionyl, pivaloyl, n-Pr, Ph and substituted Ph groups), by N-H insertion reaction of the intermediate rhodium carbenoid.

A simple route to N-acylaminophosphonoacetates (N-protected phosphonylglycine esters).

Rhodium(II) acetate catalyzed reaction of tri-Et diazophosphonoacetate with amides, carbamates or ureas gives a range of N-acyl phosphonylglycine derivs. by N-H insertion reaction of the intermediate rhodium carbenoid.

Study of the transamidative ring expansion of N--halogenoalkyl--lactams of alkyl chain lengths 2–12 in liquid ammonia and other liquid amines: syntheses of 7-, 8- and 9-membered 1,5-diaza cyclic ketones, including routes to (±)-dihydroperiphylline and (±)-celabenzine

N-(3-Halogenopropyl)-4-phenylazetidin-2-ones undergo amination in liquid ammonia followed by transamidative ring expansion to give the eight-membered 4-phenyl -1,5-diazacyclooctan-2-one in excellent yield. Ring expansion of the amines in liquid ammonia is found to be much more effective than in hydrocarbon solvents. Formation of 7-, 8-, and 9-membered azalactams from the requisite -halogenoalkyl--lactams is an excellent synthetic process, though it is not applicable to 10membered rings. In the cases of rings of 13-, 15- and 17-members, although amination and apparent expansion takes place, the large rings appear not to be stable to ammonia and the final products are acyclic amides. N-[4-Halogenobut-2(Z)-enyl]-4-phenylazetidin-2-one satisfactorily forms a 9-membered (Z)-olefinic azalactam, but the (E)-isomer gives an acyclic amino amide. By using alkyl-substituted -lactam side-chains, C-substituted medium rings can be obtained; the relative instability of N-acyl -lactams to ammonia, however, leads to acylamino amides rather than expanded rings.Employing ethylamine in place of ammonia, it is shown that N-ethylated azalactams are formed satisfactorily, and using allylamine, N-allyl medium rings capable of further elaboration are obtained. The chemistry of these systems is discussed. Using transamidation in liquid ammonia, a short synthesis of the 9-membered spermidine alkaloid (±)-dihydroperiphylline is reported. Synthesis of key intermediates, whose transformation into the 13-membered alkaloids of the celabenzine group has already been effected, has been carried out.X-Ray single-crystal structure determinations for 4-phenyl-1,5-diazacyclononan-2-one, trans-4-phenyl-8-methyl-1,5-diazacyclooctan-2-one and (Z)-4-phenyl-1,5-diazacyclonon-7-en-2-one are reported, and comment is made on certain conformational features.

Thermochemistry of Ionic Liquid-Catalyzed Reactions: Theoretical and Experimental Study of the Beckmann Rearrangement-Kinetic or Thermodynamic Control?

A thermodynamic analysis of the experimental conditions of the Beckmann rearrangement reaction of oximes into amides has been undertaken to examine whether the reaction is under thermodynamic or kinetic control. To answer this question, the thermodynamic properties of the typical Beckmann rearrangement reactions in the ideal gaseous state-cyclohexanone oxime to caprolactam and 2-butanone oxime to N-methylpropanarnide-were studied by using the quantum mechanical method. Gibbs energy and equilibrium constants of the Beckmann rearrangement have been assessed in the gaseous and the liquid phases. Results of the thermodynamic analysis have shown that Beckmann rearrange ments are kinetically controlled. Thus, a search for possible active ionic liquid based catalysts for the mild reaction conditions has been performed.

Synthesis of nucleoside analogues in a ball mill: fast, chemoselective and high yielding acylation without undesirable solvents

The chemoselective acylation of primary aliphatic amines has been achieved in under ten minutes (and for aromatic amines under 120 min) using vibration ball-milling, avoiding undesirable solvents which are typically employed for such reactions (e.g. DMF). Under optimised conditions, the synthesis of amides in the presence of both primary and secondary alcohol functions was achieved in high to excellent yields (65-94%). Overall, the methods described have significant practical advantages over conventional approaches based upon bulk solvents including greater yields, higher chemoselectivity and easier product separation.

Evaluation of Pt and Re oxidation state in a pressurized reactor: difference in reduction between gas and liquid phase

Determination of metal oxidation state under relevant working conditions is crucial to understand catalytic behaviour. The reduction behaviour of Pt and Re was evaluated simultaneously as a function of support and solvent in a pressurized reactor (autoclave). The bimetallic catalysts are used in selective hydrogenation of carboxylic acids and amides. Gas phase reduction reduced the metals more efficiently, in particular Pt.