Stereoselective synthesis of belactosin C and its derivatives using a catalytic proline catalyzed crossed-aldol reaction

A highly practical and concise stereoselective total synthesis of belactosin C and synthetic variants was achieved using an S-proline catalyzed crossed-aldol reaction as the key step.     

Synthesis and biological activity of optimized belactosin C congeners

Successful biochemical studies of the natural products belactosin A and C as well as their more stable acylated derivatives have proved them to be powerful proteasome inhibitors and thereby potential candidates as pharmacologically relevant active compounds. In order to understand their structure-biological activity relations in detail and to find ways of improving their biological activity, four new modified belactosin congeners have been synthesized and tested. One of them (compound 6) turned out to be a more potent inhibitor against HeLa cells than the known proteasome inhibitor MG132.     

Stereocontrolled synthesis of 3-(trans-2-aminocyclopropyl)alanine,a key component of belactosin A

Herein we report a concise synthesis of 3-(trans-2-aminocyclopropyl)alanine, a component of belactosin A, using asymmetric alkylation of a glycine enolate in the presence of chiral phase-transfer catalysts to control the configuration at C2. Reaction of protected glycidol with triethyl phosphonoacetate (Wadsworth-Emmons cyclopropanation) is used for enantiospecific preparation of an intermediate cyclopropanecarboxylate that is converted to a cyclopropylamine via Curtius rearrangement. [reaction: see text]     

Synthesis and biological activity of simplified belactosin C analogues

Successful biochemical studies of the natural products belactosin A and C and their acylated congeners have shown a β-lactonecarboxamide moiety to be a possible core structure of powerful proteasome inhibitors. As a part of further investigations, variously decorated simplified β-lactonecarboxamides have been synthesized in order to understand structure-biological activity relations in detail, to find ways of improving their biological activity and stability and to reduce the complexity of their preparation. Biological tests showed that the best compounds possess a high potential against phytopathogenic fungi in the greenhouse.     

Oppolzer sultam directed aldol as a key step for the stereoselective syntheses of antitumor antibiotic belactosin C and its synthetic congeners

[reaction: see text] An efficient protocol has been developed using D-(2R)-Oppolzer sultam as a chiral auxiliary for generating anti/syn diastereomers with high enantiopurity and utilized in the efficient synthesis of natural product belactosin C and their synthetic congeners. It has been observed that a variation in the stoichiometry of the Lewis acid led to a difference in anti/syn selectivity.     

Synthesis of 2,3- and 3,4-methanoamino acid equivalents with stereochemical diversity and their conversion into the tripeptide proteasome inhibitor belactosin a and its highly potent cis-cyclopropane stereoisomer

A series of chiral 2,3- and 3,4-methanoamino acid equivalents of stereochemical diversity were designed and synthesized from our chiral cyclopropane units, using a diastereoselective Grignard addition with ( R)- or ( S)- t-butanesulfinyl imines as the key step. These equivalents were converted into the proteasome inhibitor belactosin A and its cis-cyclopropane stereoisomer. The unnatural cis-isomer was shown to be more than twice as potent as belactosin A as a proteasome inhibitor.     

Synthesis of beta-cyclopropylalanines by photolysis of diacyl peroxides

[reaction: see text] Photolysis at 254 nm of neat (no solvent) unsymmetrical diacyl peroxides derived from cyclopropane carboxylic acids and l-aspartic acid generates protected beta-cyclopropylalanines in reasonable yields. Orthogonally protected 3-(trans-2-aminocyclopropyl)alanine (21), a key constituent of the antitumor agent belactosin A, as well as protected hypoglycin A (26), a causative agent of Jamaican vomiting sickness, is synthesized by this approach with coupling of the intermediate substituted cyclopropyl radicals proceeding predominantly with retention of configuration (dr >or= 95:5).     

Total synthesis of (+)-belactosin A

A concise first total synthesis of the antitumour antibiotic belactosin A is reported, involving coupling of beta-lactone carboxylic acid 3 with N-Ala-aminocyclopropyl alanine 11.     

Synthesis,X-ray structure,and properties of the singly bonded C60 dimer having diethoxyphosphorylmethyl groups utilizing the chemistry of C60(2-)

[reaction: see text] A singly bonded C60 dimer having a diethoxyphosphorylmethyl group on each C60 cage was obtained by the reaction of C60(2-) dianion with diethyl iodomethylphosphonate followed by the treatment with iodine. The precise structure of the dimer was determined for the first time by X-ray crystallography, and its homolytic dissociation as well as spectroscopic and electrochemical properties were clarified.     

Synthesis, structure, and 19F NMR spectra of 1,3,7,10,14,17,23,28,31,40-C60(CF3)10

A significant improvement in the selectivity of fullerene trifluoromethylation reactions was achieved. Reaction of trifluoroiodomethane with [60]fullerene at 460 degrees C and [70]fullerene at 470 degrees C in a flow reactor led to isolation of cold-zone-condensed mixtures of C60(CF3)n and C70(CF3)n compounds with narrow composition ranges: 6 < or = n < or = 12 for C(60)(CF3)n and 8 < or = n < or = 14 for C70(CF3)n. The predominant products in the C(60) reaction, an estimated 40+ mol % of the cold-zone condensate, were three isomers of C60(CF3)10. Two of these were purified by two-stage HPLC to 80+% isomeric purity. The third isomer was purified by three-stage HPLC to 95% isomeric purity. Thirteen milligrams of this orange-brown compound was isolated (5% overall yield based on C60, and its C1-symmetric structure was determined to be 1,3,7,10,14,17,23,28,31,40-C60(CF3)10 by X-ray crystallography. The CF3 groups are either meta or para to one another on a p-m-p-p-p-m-p-m-p ribbon of edge-sharing C6(CF3)2 hexagons (each pair of adjacent hexagons shares a common CF3 group). The selectivity of the C70 reaction was even higher. The predominant product was a single C70(CF3)10 isomer representing >40 mol % of the cold-zone condensate. Single-stage HPLC led to the isolation of 12 mg of this brown compound in 95% isomeric purity (27% overall yield based on converted C70. The new compounds were characterized by EI or S(8)-MALDI mass spectrometry and 2D-COSY 19F NMR spectroscopy. The NMR data demonstrate that through-space coupling via direct overlap of fluorine orbitals is the predominant contribution to J(FF) values in these and most other fullerene(CF3)n compounds.     

Zn(OTf)2-catalyzed cyclization of proparyl alcohols with anilines, phenols, and amides for synthesis of indoles, benzofurans, and oxazoles through different annulation mechanisms

Zn(OTf)2 (10 mol %) catalyzed the cyclization of propargyl alcohols with PhXH (X = O, NH) in hot toluene (100 degrees C) without additive and gave indole and benzofuran products with different structures. In such transformations, alpha-carbonyl intermediates A and C were isolated as reaction intermediates. The 1,2-nitrogen shift in the formation of indole is catalyzed by Zn(OTf)2, and its mechanism has been elucidated. This catalytic cyclization is also applicable to the synthesis of oxazoles through the cyclization of propargyl alcohols and amides without a 1,2-nitrogen shift.     

A Minimal β‐Lactone Fragment for Selective β5c or β5i Proteasome Inhibitors

Broad‐spectrum proteasome inhibitors are applied as anticancer drugs, whereas selective blockage of the immunoproteasome represents a promising therapeutic rationale for autoimmune diseases. We here aimed at identifying minimal structural elements that confer β5c or β5i selectivity on proteasome inhibitors. Based on the natural product belactosin C, we synthesized two β‐lactones featuring a dimethoxybenzyl moiety and either a methylpropyl (pseudo‐isoleucin) or an isopropyl (pseudo‐valine) P1 side chain. Although the two compounds differ only by one methyl group, the isoleucine analogue is six times more potent for β5i (IC₅₀=14 nM ) than the valine counterpart. Cell culture experiments demonstrate the cell‐permeability of the compounds and X‐ray crystallography data highlight them as minimal fragments that occupy primed and non‐primed pockets of the active sites of the proteasome. Together, these results qualify β‐lactones as a promising lead‐structure motif for potent nonpeptidic proteasome inhibitors with diverse pharmaceutical applications.     

A Direct,Concise, and Enantioselective Synthesis of 2‐Substituted 4,4,4‐Trifluorobutane‐1,3‐diols Based on the Organocatalytic In Situ Generation of Unstable Trifluoroacetaldehyde

A direct, concise, and enantioselective synthesis of 2‐substituted 4,4,4‐trifluorobutane‐1,3‐diols based on the organocatalytic asymmetric direct aldol reaction of an ethyl hemiacetal of trifluoroacetaldehyde with various aldehydes was examined. A catalytic amount (30 mol %) of commercially available and inexpensive l ‐prolinamide is quite effective as an organocatalyst for the catalytic in situ generation of gaseous and unstable trifluoroacetaldehyde from its hemiacetal, and a successive asymmetric direct aldol reaction with various aldehydes in dichloromethane at 0 °C, followed by reduction with sodium borohydride, gives 2‐substituted 4,4,4‐trifluorobutane‐1,3‐diols in moderate to good yields (31–84 %) with low diastereoselectivities and good to excellent enantioselectivities (64–97 % ee).     

A novel sublimable organic salt: Synthesis,characterization, thermal behavior,and catalytic activity for the synthesis of arylidene,heteroarylidene, and alkylidene malonates

A novel sublimable organic salt was synthesized, and its chemical structure was characterized by FTIR, 1D NMR, 2D NMR, and elemental analysis. In addition, the thermal phase transitions and thermal stability of new organic salt were investigated. The DSC and TGA results showed that the organic salt could convert into constituent molecules at?<?145 °C before decomposition temperature (T_dec.?~?200 °C) under atmospheric pressure without forming the liquid phase. Then, it was recondensed to regenerate the initial organic salt in the cool part of the vial. Therefore, it can be a promising organic salt towards the regeneration of spent catalyst from synthesis processes when the reaction mixture contains poorly volatile components and includes its use in gas-phase procedures. Also, the catalytic efficiency of new organic salt was investigated in the Knoevenagel condensation reaction. A variety of substituted arylidene and alkylidene malonates were isolated in 78–95% yield within six hours.? Under the optimized reaction conditions, the current catalytic procedure exhibited superiority compared to the mixed piperazine/acetic acid, piperidine/acetic acid, and piperidinium acetate. There were no significant changes in the new organic salt chemical structure and catalytic activity even after the 5th run. This work revealed the importance of the existence of simultaneous hydrogen bond acceptor/donor groups in our environmentally friendly catalyst to promote the Knoevenagel condensation reaction without the use of metal-containing catalysts.

     

Simultaneous determination of prostaglandins E1, A1, and B1 by reversed-phase high-performance liquid chromatography for the kinetic studies of prostaglandin E1 in solution.

A method for the simultaneous determination of prostaglandins E1, A1 and B1 (PGE1, PGA1 and PGB1) in solution has been developed by reversed-phase high-performance liquid chromatography using a 3 microns C18 column. The mobile phase consisted of 35% acetonitrile in 0.002 M phosphate buffer (pH 3.5) and its flow-rate was 1.5 ml/min. Quantitative measurement was performed using a photodiode array detector system at 190, 220, and 280 nm for PGE1, PGA1 and PGB1, respectively. The method has been applied to the primary kinetic studies for reaction profile for PGE1----PGA1----PGB1 at 60 degrees C in pH 2.0, 7.2, 10.0 and 12.0 buffer solutions.     

Poly-2-vinylfuran,synthesis, characterization,and diels-alder reaction with maleic anhydride

Poly-2-vinylfuran, synthesized by free-radical polymerization of 2-vinylfuran, was characterized by nuclear magnetic resonance (NMR) and infrared (IR) spectroscopy. The pendant furan rings on the polymer backbone were then used as the diene component of a Diels-Alder reaction with maleic anhydride. The juxtaposition of the furan rings at first suggested an “avalanche” Diels-Alder reaction, in which the product of one cyclization would be the reactant of the next. A lack of polymer stereoregularity and the reversibility of the Diels-Alder reaction, however, prevented its formation. On the other hand, when the dienophile was used in a 1:1 molar ratio with respect to furan the smooth reaction produced a new polymer, the maleic anhydride adduct of poly-2-vinylfuran, which characterized by NMR and IR spectroscopy, was air stable and soluble in a number of solvents up to 70% transformation. When heated to 160°C the polymer reverted to maleic anhydride and somewhat decomposed poly-2-vinylfuran.     

Cloning, expression, and characterization of thermostable region of amylopullulanase gene from Thermoanaerobacter ethanolicus 39E

The bifunctional activities of α-amylase and pullulanase are found in the cloned recombinant amylopullulanase. It was encoded in a 2.9-kb DNA fragment that was amplified using polymerase chain reaction from the chromosomal DNA of Thermoanaerobacter ethanolicus 39E. An estimated 109-kDa recombinant protein was obtained from the cloned gene under the prokaryotic expression system. The optimum pH of the recombinant amylopullulanase was 6.0. The most stable pH for the α-amylase and pullulanase activity was 5.5 and 5.0, respectively. The optimum temperature for the α-amylase activity was 90°C, while its most stable temperature was 80°C. Regarding pullulanase activity, the optimum temperature and its most stable temperature were found to be 80 and 75°C, respectively. Pullulan was found to be the best substrate for the enzyme. The enzyme was activated and stabilized by the presence of Ca²⁺, whereas EDTA, N-bromosuccinimide, and α-cyclodextrin inhibited its bifunctional activities. A malto-2–4-oligosac-charide was the major product obtained from the enzymatic reaction on soluble starch, amylose, amylopectin, and glycogen. A single maltotriose product was found in the pullulan hydrolysis reaction using this recombinant amylopullulanase. Kinetic analysis of the enzyme indicated that the K _m values of α-amylase and pullulanase were 1.38 and 3.79 mg/mL, respectively, while the V _max values were 39 and 98 μmol/(min · mg of protein), respectively.     

Studies on the oxidative addition reaction of 1,1-dibromo-1-alkenes, alpha-dehalopalladation, and the intramolecular bis(carbopalladation) reaction of alkenes. An efficient entry to fused bicycles

Twenty-three examples of 1,1-dihalo-1-alkenes were synthesized by the conventional alkylation methods. The oxidative addition reactions of 1,1-dibromo-2,2-diphenylethene or 1, 1-dibromo-2-phenylpropene with a stoichiometric amount of Pd(PPh(3))(4) afforded 1,2-diphenylacetylene and 1-phenylpropyne, respectively, indicating that alpha-dehalopalladation reaction occurred to afford vinylic carbene intermediates. However, alpha-dehalopalladation reaction was not observed in all 1, 1-dihalo-1-alkenes containing an extra C=C bond suitable for cyclic carbopalladation under the current reaction conditions probably due to the fast cyclic carbopalladation reaction of 40A-type of palladium intermediates; A series of bicycles, i.e., fused 5,6-, 6, 6-, 6,7-, and 7,7-bicyclic compounds, were prepared efficiently via this bicyclic carbopalladation protocol. Under condition A, within 0. 5 h, 10 afforded the monocyclic product 37 in 79%. With prolonged reaction time, 37 was converted to bicycle 36. Even with isolated 37, the corresponding reaction under condition A afforded 36 in 92% NMR yield, indicating a stepwise oxidative addition-cyclic carbopalladation-beta-elimination mechanism for this bicyclization reaction.     

Nickel,cobalt, and Ni-Co alloy nanopowders prepared by plasma-assisted milling: Catalytic activity in the carbon dioxide reforming of methane

The nanopowders of Ni and Co metals and their alloy were prepared by plasma-assisted milling, and the activity of catalysts on their basis was studied in the carbon dioxide reforming of methane (CDRM) at atmospheric pressure. It was found that the catalytic activity of Ni nanopowder rapidly decreased because of the blocking of its surface by coking products. Co powder exhibited lower but stable activity, which gradually decreased as a result of coking only 300 h after the onset of reaction. A Ni-Co alloy (1: 1, by weight) is an active and selective catalyst for CDRM. Its catalytic activity appeared at 400°C; at 870°C, conversion reached 90% and remained unchanged for 500 h. The initial activity was restored by the regeneration of a catalyst based on the Ni-Co alloy with molecular hydrogen for several hours at 400°C.     

Reaction of Cl atoms with C6F13CH2OH, C6F13CHO, and C3F7CHO

The Cl atom initiated oxidation of C(6)F(13)CH(2)OH, C(6)F(13)CHO, and C(3)F(7)CHO was investigated at 298 K and 1000 mbar pressure of air in a photoreactor using in situ Fourier transform infrared (FTIR) analysis. The rate coefficient for the reaction Cl + C(6)F(13)CH(2)OH (reaction 2) was measured using a relative method: k(2) = (6.5 +/- 0.8) x 10(-13) cm(3) molecule(-1) s(-1). C(6)F(13)CHO was detected as the major primary product, while CO and CF(2)O were found to be the major secondary products. A fitting procedure applied to the concentration-time profiles of C(6)F(13)CHO provided a production yield of (1.0 +/- 0.2) for this aldehyde in reaction 2, and the rate coefficient for the reaction Cl + C(6)F(13)CHO (reaction 4) was k(4) = (2.8 +/- 0.7) x 10(-12) cm(3) molecule(-1) s(-1). A high CO yield observed in the oxidation of C(6)F(13)CH(2)OH, (52 +/- 1)%, is attributed to the Cl atom initiated oxidation of C(6)F(13)CHO. High CO yields, (61 +/- 2)% and (85 +/- 5)%, were also measured in the Cl atom initiated oxidation of C(3)F(7)CHO in air and nitrogen, respectively. These high CO yields suggest the occurrence of a decomposition reaction of the perfluoroacyl, C(6)F(13)CO, and C(3)F(7)CO radicals to form CO which will compete with the combination reaction of these radicals with oxygen to form perfluoroacyl peroxy radicals in the presence of air. The latter radicals C(n)F(2)(n)(+1)CO(O)(2) (n = 6-12), through their reaction with HO(2) radicals, are currently considered as a possible source of persistent perfluorocarboxylic acids which have been detected in the environment. The consequences of the present results would be a reduction of the strength of this potential source of carboxylic acids in the atmosphere.