Backbone amide linker (BAL) strategy for Nalpha-9-fluorenylmethoxycarbonyl (Fmoc) solid-phase synthesis of peptide aldehydes.

A rapid and efficient strategy has been developed for the general synthesis of complex peptide aldehydes. N(alpha)-Benzyloxycarbonylamino acids were converted to protected aldehyde building blocks for solid-phase synthesis in four steps and moderate overall yields. The aldehydes were protected as 1,3-dioxolanes except for one case where a dimethyl acetal was used. These protected amino aldehyde monomers were then incorporated onto 5-[(2 or 4)-formyl-3,5-dimethoxyphenoxy]butyryl-resin (BAL-PEG-PS) by reductive amination, following which the penultimate residue was introduced by HATU-mediated acylation. The resultant resin-bound dipeptide unit, anchored by a backbone amide linkage (BAL), was extended further by routine Fmoc chemistry procedures. Several model peptide aldehydes were prepared in good yields and purities. Some epimerization of the C-terminal residue occurred (10% to 25%), due to the intrinsic stereolability conferred by the aldehyde functional group, rather than any drawbacks to the synthesis procedure.     

Pyruvate aldolases in chiral carbon-carbon bond formation

A procedure for the preparation of optically pure alpha-keto-gamma-hydroxy carboxylic acids through stereospecific aldol addition catalyzed by pyruvate aldolases from the Entner-Doudoroff and the DeLey-Doudoroff glycolytic pathways is described. This highly versatile fragment serves as a precursor for a variety of commonly encountered functionalities, including beta-hydroxy aldehydes and carboxylic acids, alpha-amino-gamma-hydroxy carboxylic acids and alpha,gamma-dihydroxy carboxylic acids. The protocol described here uses recombinant His6-tagged KDPG aldolase for the synthesis of (S)-4-hydroxy-2-keto-4-(2'-pyridyl)butyrate. A protocol for evaluating enantiomeric excess through formation of the gamma-lactone of the dithioacetal followed by chiral-phase gas-liquid chromatography is also described. Enzyme expression and enzymatic synthesis can be accomplished in approximately 1 week. The enzymatic aldol addition proceeds in nearly quantitative yields with enantiomeric excesses greater than 99.7%.     

Asymmetric aldol reaction using boron enolates

The protocol for the preparation of boron enolates and their subsequent reaction with aldehydes is described, providing convenient access to beta-hydroxy ketones in good yields and with high stereoselectivities. The reaction consists of three steps: first, the ketone is rapidly converted to the corresponding boron enolate, by exposure to a chlorodialkylborane and tertiary amine base, which is then reacted in situ with the aldehyde. Finally, oxidative workup of the resultant boron aldolate provides aldol adduct. The reaction procedure requires approximately 28 h to complete over a 2-d period, consisting of 5 h to set up the reaction, whereupon the reaction mixture is left at -20 degrees C overnight (16 h), followed by 7 h for workup and purification.     

Brønsted Acid Promoted Facile Synthesis of Benzoacridines from Aromatic Aldehydes and N-Phenyl Naphthylamines

A facile method for the rapid synthesis of benzoacridines has been described. This protocol promoted by p-toluenesulfonic acid starts from aromatic aldehydes and N-phenyl naphthylamines, affording a variety of benzoacridines in 30–90 % yields under metal-free conditions. The present approach involves a cascade of condensation, Friedel-Crafts alkylation, annulation and dehydroaromatization in one pot.     

Immobilization of fuculose-1-phosphate aldolase from E. coli to glyoxal-agarose gels by multipoint covalent attachment

Recombinant fuculose 1-phosphate aldolase (FucA) from E. coli has been immobilized by multipoint covalent attachment to glyoxal-agarose gels. Experiments, varying the main parameters that control the immobilization process (surface density of aldehyde groups, temperature, pH), were carried out. An immobilization yield of 80-90% and FucA retained activity on immobilized derivative of 10-20% can be achieved when pH 10, 20°C and 200 µmoles cm^-3 of aldehyde groups was used. The observed activity loss in the immobilization process might be related to the fact that the complex quaternary structure of the enzyme could not be maintained. A short contact-time enzyme support is required to obtain high ratio of active to total immobilized enzyme.


A highly loaded derivative of immobilized FucA (65 AU cm^-3 of support) has been prepared to use in aldol condensation reactions. Reactions catalyzed by these aldolases involve the use of non-conventional media because of substrate solubility. For instance, the condensation of dihydroxyacetone phosphate (DHAP) and Z-amino-propanal, Z-(R)-alaninal and Z-(S)- alaninal in highly concentrated water-in-oil emulsions gave synthetic yields of 40, 25 and 29% respectively.     

Immobilization of fuculose-1-phosphate aldolase from E. coli to glyoxal-agarose gels by multipoint covalent attachment

Recombinant fuculose 1-phosphate aldolase (FucA) from E. coli has been immobilized by multipoint covalent attachment to glyoxal-agarose gels. Experiments, varying the main parameters that control the immobilization process (surface density of aldehyde groups, temperature, pH), were carried out. An immobilization yield of 80–90% and FucA retained activity on immobilized derivative of 10–20% can be achieved when pH?10, 20°C and 200?µmoles?cm^?3 of aldehyde groups was used. The observed activity loss in the immobilization process might be related to the fact that the complex quaternary structure of the enzyme could not be maintained. A short contact-time enzyme support is required to obtain high ratio of active to total immobilized enzyme.

A highly loaded derivative of immobilized FucA (65?AU?cm^?3 of support) has been prepared to use in aldol condensation reactions. Reactions catalyzed by these aldolases involve the use of non-conventional media because of substrate solubility. For instance, the condensation of dihydroxyacetone phosphate (DHAP) and Z-amino-propanal, Z-(R)-alaninal and Z-(S)- alaninal in highly concentrated water-in-oil emulsions gave synthetic yields of 40, 25 and 29% respectively.     

Use of secondary isotope effects and varying pH to investigate the mode of binding of inhibitory amino aldehydes by leucine aminopeptidase

Ki values for leucine aldehyde, a competitive inhibitor of leucine aminopeptidase, vary with pH in a manner compatible with binding of uncharged inhibitor. The pH dependence of kcat/Km suggests likewise that the substrate leucine p-nitroanilide is productively bound as the uncharged species. Comparison of pKa values of the model compounds aminoacetone and aminoacetal indicates that the equilibrium constant for hydration of amino aldehydes is reduced by a factor of about 2 when a proton is lost from the alpha-ammonium group near pH 8. Effects of deuterium substitution at C-1 on equilibrium binding of leucine aldehyde were determined with immobilized enzyme and inhibitors doubly labeled with radioisotopes. The observed isotope effect (KD/KH) is approximately unity, suggesting that leucine aldehyde combines with the enzyme as an oxygen adduct, not as the intact aldehyde.     

Oxime-based linker libraries as a general approach for the rapid generation and screening of multidentate inhibitors

The described oxime-based library protocol provides detailed procedures for the linkage of aminooxy functionality with aldehyde building blocks that result in the generation of libraries of multidentate inhibitors. Synthesis of inhibitors for protein tyrosine phosphatases (PTPs) and antagonists directed against the human tumor susceptibility gene 101 (TSG101) are shown as examples. Three steps are involved: (i) the design and synthesis of aminooxy platforms; (ii) tethering with aldehydes to form oxime-based linkages with sufficient purity; and (iii) direct in vitro biological evaluation of oxime products without purification. Each coupling reaction is (i) performed in capped microtubes at room temperature (20-23 °C); (ii) diluted for inhibitory evaluation; and (iii) screened with targets in microplates to provide IC(50) or K(d) values. The synthesis of the aminooxy platforms takes 3-5 d; tethering with the aldehydes takes 24 h; and inhibition assay of enzymes and protein-protein interactions takes 30 min and 2 h, respectively.     

An example of enzymatic promiscuity: the Baylis–Hillman reaction catalyzed by a biotin esterase (BioH) from Escherichia coli

Ten lipases and esterases have been examined to catalyse the reaction between p-nitrobenzaldehyde and methyl vinyl ketone, the Baylis–Hillman reaction, to form 3-[hydroxyl-(4-nitrophenyl)-methyl]-but-3-en-2-one. Among these enzymes, Escherichia coli BioH esterase had the best activity. Optimal conditions for this reaction were: 0.1 mmol aldehyde, 0.1 mmol activated alkene, 30 mg E. coli BioH, 1 ml acetonitrile at 30 °C for 96 h. In addition to the named substrates, four other aldehydes and three activated alkenes were also investigated to determine the substrate range of the enzyme. The structures of nine products were confirmed by NMR and yields of the corresponding products ranged from 21 to 46 %.     

由有机硼烷合成桃小食心虫性信息素 Z-7-二十烯-11-酮和 Z-7-十九烯-11-酮

研究了用有机硼烷的转化反应立体选择合成 Z-4-十一烯-1-醛(7)以及将其应用于桃小食心虫性信息素 Z-7-11-二十烯-11-酮(1)和 Z-7-十九烯-11-酮(2)的简便合成方法。用前文报告的经由有机硼烷一锅反应制备法获得的 Z-4-十一烯-1-醇(6),经氯铬酸吡啶(PCC)氧化生成 Z-4-十一烯-1-醛(7),后者与 Grignard 试剂作用,得中间物仲醇 Z-7-链烯-11-醇(8),然后使之氧化,即得预期的 Z-7-链烯-11-酮(1)和(2)。从起始原料1-已烯出发,总产率分别为36.9％和35.0％.     

Different forms of rat liver aldehyde dehydrogenase and their subcellular distribution.

1. The properties and distribution of the NAD-linked unspecific aldehyde dehydrogenase activity (aldehyde: NAD+ oxidoreductase EC 1.2.1.3) has been studied in isolated cytoplasmic, mitochondrial and microsomal fractions of rat liver. The various types of aldehyde dehydrogenase were separated by ion exchange chromatography and isoelectric focusing. 2. The cytoplasmic fraction contained 10-15, the mitochondrial fraction 45-50 and the microsomal fraction 35-40% of the total aldehyde dehydrogenase activity, when assayed with 6.0 mM propionaldehyde as substrate. 3. The cytoplasmic fraction contained two separable unspecific aldehyde dehydrogenases, one with high Km for aldehydes (in the millimolar range) and the other with low Km for aldehydes (in the micromolar range). The latter can, however, be due to leakage from mitochondria. The high-Km enzyme fraction contained also all D-glucuronolactone dehydrogenase activity of the cytoplasmic fraction. The specific formaldehyde and betaine aldehyde dehydrogenases present in the cytoplasmic fraction could be separated from the unspecific activities. 4. In the mitochondrial fraction there was one enzyme with a low Km for aldehydes and another with high Km for aldehydes, which was different from the cytoplasmic enzyme. 5. The microsomal aldehyde dehydrogenase had a high Km for aldehydes and had similar properties as the mitochondrial high-Km enzyme. Both enzymes have very little activity with formaldehyde and glycolaldehyde in contrast to the other aldehyde dehydrogenases. They are apparently membranebound.     

A Novel Oxazolidine Linker for the Synthesis of Peptide Aldehydes

A reliable method for solid-phase synthesis of peptide aldehydes by using a new oxazolidine linker is described. Based on a comparative study using the usual cleavage protocol as is used for the Fmoc-based peptide synthesis, we found that this new linker is more appropriate for the synthesis of peptide aldehydes compared with the precedent acetal, semicarbazone or threonine linker. Whereas N-Acylated oxazolidines might be partially deprotected to non-N-acylated intermediates in the TFA cocktail containing several soft nucleophiles which cause significant side reactions, the new oxazolidine linker could produce the desired peptide aldehydes by simple Et₂O washing and subsequent aqueous workup in high chemical yields and purity. We demonstrate the new method is useful especially for the preparation of highly functionalized long-chain peptide aldehydes which require several scavenger chemicals in the final deprotection step. This paper is dedicated to the memory of the late Prof. R. Bruce Merrifield, who passed away May 14, 2006.     

Reductive and oxidative synthesis of saturated and unsaturated fatty aldehydes

Saturated and unsaturated fatty aldehydes were synthesized 99+% pure with yields of up to 80% by the reduction of 1-acylaziridines with lithium aluminium hydride, and in yields of up to 87% by oxidation of the corresponding alcohol with 1-chlorobenzotriazole. It was found for the reduction that optimum aldehyde yield was obtained with a mole ratio of reactants, consisting of acid chloride-ethylenimine-triethylamine-LiAlH(4), equal to 1:2:2:2. Optimum conditions for alcohol oxidation were found to be a mole ratio of oxidant to alcohol of 1:1.3 with refluxing for 45 min in methylene chloride containing 25% pyridine. Methods for the purification of the final product are also described. Purity criteria were thin-layer and gas-liquid chromatography and infrared and nuclear magnetic resonance spectroscopy.     

Practical Proline-catalyzed asymmetric Mannich reaction of aldehydes with N-Boc-imines

This protocol describes a procedure for the synthesis of alpha, beta-branched-b-amino aldehydes via Proline-catalyzed asymmetric Mannich reaction of aldehydes with N-tert-butoxycarbonyl-imines. The crystalline beta-amino aldehydes are formed in good yields and extremely high levels of diastereo- and enantioselectivities without the need for chromatographic purification and are readily oxidized to the corresponding beta-amino acids. The protocol can be completed in approximately 14 h on small scales or up to 30 h on larger scales.     

Triflimide (HNTf2)-catalyzed aldehyde cross-aldol reaction using "super silyl" enol ethers

The synthesis of the acetaldehyde-derived tris(trimethylsilyl)silyl (super silyl) enol ether is described, as well as its use in the high-yielding aldehyde cross-aldol reaction. The super silyl enol ether shows unprecedented reactivity in giving the 1:1 adduct in very high yield. This reaction is catalyzed by 0.05 mol% of the Br?nsted acid triflimide (HNTf2) and is complete within 15 min, making the protocol very attractive for large-scale synthesis.     

棉铃虫性外激素成分的化学分析和田间试验

利用毛细柱的气相色谱和质谱对棉铃虫（鳞翅目：夜蛾科）雌蛾腺体提取物的分析,鉴定出了他和十六碳醛、顺－9－十六碳烯醛、顺－11－十六碳烯醛、饱和十六碳醇和顺－11－十六碳烯醇,其相对比例为6．1：4．5：100：3．5：8．8。在山东、山西省的田间试验中,2mg的顺－11－十六碳烯醛和顺－9－十六碳烯醛（97：3）置橡胶塞上能有效地引诱棉铃虫雄蛾。增加4％－7％他和十六碳醛到二元混合物中诱蛾量超过二元混合物。增加1％顺－11－十六碳烯醇到二元或三元混合物中减少诱蛾量,当增加5％顺－11－十六碳醇时诱蛾量大量减少。     

The effect of aldehyde fixation on selected substrates for energy metabolism and amino acids in mouse brain.

The effect of aldehyde fixation on concentrations of low molecular weight constituents was determined by comparing amounts of selected intermediates in brains of mice exposed to aldehyde fixative solutions with those perfused with phosphate buffer solution alone. Aldehyde perfusion resulted in excellent preservation of cerebral cortex ultrastructure in the presence of dramatic declines in adenosine triphosphate, phosphocreatine, glucose and glucose-6-phosphate that occureed before exposure of the tissue to aldehyde fixatives. Decreases in hexose were accompanied by approximately a 4-fold increase in lactate and a 2-fold increase in pyruvate. Glycogen levels decreased by about 60% during the initial operative procedure but remained constant after aldehyde fixation. Glycogen content declined approximately 90% in tissues that were not treated with aldehyde. Concentrations of aspartate and glutamate changed only slightly during the initial period (1-5 min) and remained constant for at least 90 min in cerebral cortices fixed with aldehydes. Alanine levels increased in both fixed and unfixed tissue; however, this increase was much smaller in tissues exposed promptly to aldehydes. Total ninhydrin-positive material in perchloric acid extracts of brain decreased in mice exposed to aldehyde solutions but increased in tissues that were not. These results indicated that several amino acids may be measured reliably in tissues preserved for light and electron microscopy. In addition, determination of glutamate: alanine ratios in tissues perfused with aldehydes may provide an indication of the timing of fixation.     

Core aldehydes of alkyl glycerophosphocholines in atheroma induce platelet aggregation and inhibit endothelium-dependent arterial relaxation.

Plaque disruption with superimposed thrombosis is considered to be responsible for precipitating acute coronary syndrome. We identified sn-1-alkyl- and sn-1-acyl-type glycerophosphocholine (GroPCho) core aldehydes from human atheromas and demonstrated their activities on platelets and arteries. The naturally occurring core aldehydes were identified and quantified in relation to synthetic standards by high performance liquid chromatography with on-line electrospray mass spectrometry. 1-O-Hexadecyl-2-(5-oxovaleroyl)-sn-GroPCho (C(5) alkyl GroPCho core aldehyde), occurring in atheroma at less than 0.1% of total phosphatide, induced aggregation of washed rabbit platelets (50% effective dose was approximately 50 nM). Aggregations induced by C(5) alkyl GroPCho core aldehydes were completely inhibited by two different platelet-activating factor receptor antagonists. 1-Palmitoyl-2-(5-oxovaleroyl)-sn-GroPCho (C(5) acyl GroPCho core aldehyde) induced platelet shape change, but not aggregation. By contrast, 10 microM C(5) alkyl and C(5) acyl GroPCho core aldehydes both inhibited endothelium-dependent relaxation of rabbit artery by 50% (endothelium-independent relaxation was not affected). The present demonstration of platelet aggregation by physiologically relevant concentrations of alkyl GroPCho core aldehydes suggests that alkyl GroPCho core aldehyde generated in atheroma could be involved in precipitating acute coronary events, in which thrombus formation following lipid-rich plaque disruption plays an important role.     

Hydrolytic enzyme substrates. I. Chemical synthesis and characterization

The synthesis and characterization of a number of new phosphate, sulfate and acetate esters of 3-(p-nitrophenoxy)-1,2-propanediol (PNG); 3-(2,4-dinitrophenoxy)-1,2-propanediol (DNG); 4-(p-nitrophenoxy)-1,2-butanediol (PNB) and 4-(2,4-dinitrophenoxy)-1,2-butanediol (DNB) are described. These esters were prepared to serve as substrates for their corresponding hydrolytic enzymes. The assay system used to measure enzyme hydrolysis requires periodate oxidation of the diol formed after hydrolysis of the ester. Base treatment of the resulting aldehyde yields either p-nitrophenolate ion or the 2,4-dinitrophenolate ion depending upon the substrate. In the presence of high concentrations of methylamine and excess periodate the oxidation and elimination reactions can be carried out simultaneously at pH 7.5. The reactions leading to these results are described.     

L-proline-catalyzed enantioselective one-pot cross-Mannich reaction of aldehydes

This protocol describes a procedure for the synthesis of syn-beta-amino alpha-substituted aldehydes, versatile intermediates in synthetic organic chemistry, via asymmetric, direct, one-pot, three-component, cross-Mannich reaction of two different aldehydes. The reaction consists of two steps; one is the formation of imine by the reaction of aldehyde and p-anisidine in the presence of Pro, and the second step is the enantioselective addition reaction of enamine generated from the other aldehyde and Pro with the imine generated in the first step. As the aldehyde easily racemizes, gamma-amino alcohol was isolated and characterized after reduction. The yield and diastereo- and enantioselectivities are generally excellent. It will take approximately 26 h to complete the protocol: 0.5 h to set up the reaction, 20.5 h for the reaction and 5 h for the isolation and purification.