Anthony J. Burke

Thermostabilization of Proteins by Diglycerol Phosphate, a New Compatible Solute from the Hyperthermophile Archaeoglobus fulgidus

ABSTRACT Diglycerol phosphate accumulates under salt stress in the archaeonArchaeoglobus fulgidus (L. O. Martins, R. Huber, H. Huber, K. O. Stetter, M. S. da Costa, and H. Santos, Appl. Environ. Microbiol. 63:896–902, 1997). This solute was purified after extraction from the cell biomass. In addition, the optically active and the optically inactive (racemic) forms of the compound were synthesized, and the ability of the solute to act as a protecting agent against heating was tested on several proteins derived from mesophilic or hyperthermophilic sources. Diglycerol phosphate exerted a considerable stabilizing effect against heat inactivation of rabbit muscle lactate dehydrogenase, bakers yeast alcohol dehydrogenase, andThermococcus litoralis glutamate dehydrogenase. Highly homologous and structurally well-characterized rubredoxins fromDesulfovibrio gigas, Desulfovibrio desulfuricans (ATCC 27774), and Clostridium pasteurianum were also examined for their thermal stabilities in the presence or absence of diglycerol phosphate, glycerol, and inorganic phosphate. These proteins showed different intrinsic thermostabilities, with half-lives in the range of 30 to 100 min. Diglycerol phosphate exerted a strong protecting effect, with approximately a fourfold increase in the half-lives for the loss of the visible spectra of D. gigas and C. pasteurianumrubredoxins. In contrast, the stability of D. desulfuricansrubredoxin was not affected. These different behaviors are discussed in the light of the known structural features of rubredoxins. The data show that diglycerol phosphate is a potentially useful protein stabilizer in biotechnological applications.

Advances in the Catalytic Asymmetric Arylation of Imines using Organoboron Reagents: An Approach to Chiral Arylamines

The production of chiral amines by means of catalytic asymmetric synthesis is a current challenge in the field of drug discovery and is discussed in this review. The use of cheap, easily handled, and low toxic organoboron reagents, such as boronic acids and derivatives, and easily prepared imine substrates, such as diphenylphosphinoyl, N‐Boc, N‐tosylaryl, N‐nosylaryl, or dimethylsulfamoyl imines, together with rhodium and palladium catalysts give the corresponding chiral amine products in excellent yields and enantioselectivities. A diverse range of chiral ligands, such as phosphines, phosphites, phosphoramidites, P,O‐ligands, olefins, NHCs, and N,N‐ligands can be used with this method, showing, therefore, its versatility. The application of aliphatic imine substrates and with the use of different palladium complexes show, on the other hand, the versatility of the method described.

Asymmetric synthesis of (2S,3R)-3-amino-2-hydroxydecanoic acid: The unknown amino acid component of microginin

Abstract 3-Amino-2-hydroxydecanoic acid (AHDA) is an unusual amino acid purported to occur in the recently isolated angiotensin-converting enzyme inhibitor microgipin. In order to elucidate the stereochemistry of the naturally occurring material, and thus complete the structural assignment of microginin, both the (2 R ,3 R )- anti -diastereoisomer and the (2 S ,3 R ) syn -diastereoisomer of AHDA have been prepared. Comparison of the 1 H and 13 C nmr spectroscopic data of the synthetic amino acids with that reported for the naturally occurring material indicates that the relative stereochemisuy of the AHDA found in microginin is syn . The absolute stereochemistry of the natural amino acid is shown to be (2 S ,3 R ) by comparison of its reported CD spectrum with that recorded for the synthetic material prepared herein.

Asymmetric synthesis and applications of β-amino Weinreb amides: asymmetric synthesis of (S)-coniine

Conjugate addition of lithium (S)-N-benzyl-N-alpha-methylbenzylamide to a range of alpha, beta-unsaturated Weinreb amides proceeds with high levels of diastereoselectivity (>95% de). The beta-amino Weinreb amide products may be transformed into beta-amino ketones via reactions with Grignard reagents, while treatment with DIBAL-H furnishes beta-amino aldehydes. Trapping of the aldehyde via Wadsworth-Emmons reaction and subsequent manipulation offers an efficient route to homochiral delta-amino acid derivatives and 2-substituted piperidines. The application of this methodology for the synthesis of (S)-coniine is demonstrated.

Asymmetric synthesis of the N-terminal component of microginin: (2S,3R)-3-amino-2-hydroxydecanoic acid, its (2R,3R)-epimer and (3R)-3-aminodecanoic acid

Abstract 3-Amino-2-hydroxydecanoic acid (AHDA) is a novel amino acid which has been suggested as the N -terminal component of the recently isolated angiotensin-converting enzyme inhibitor microginin. The naturally occurring amino acid was found to possess syn relative stereochemistry and (2 S ,3 R ) absolute stereochemistry when the reported 1 H and 13 C nmr spectroscopic data and the CD data were compared to the spectroscopic data for synthetic (2 R ,3 R )- and (2 S ,3 R )-AHDA. These studies complete the stereochemical assignment of microginin.

Aspects of the Algar-Flynn-Oyamada (AFO) reaction

Abstract The oxidation of 2′-hydroxychalcones 1 with alkaline hydrogen peroxide, commonly known as the Algar, Flynn and Oyamada (AFO) reaction is a convenient method for the synthesis of 2-aryl-3-hydroxy-4H-1-benzopyran-4-ones (flavonols), 2-aryl-2,3-dihydro-3-hydroxy-4H-1-benzopyran-4-ones (2,3-dihydroflavonols), 2-arylidenebenzo[b]furan-3(2H)-ones (aurones) and other flavonoid compounds. Oxidation of substrates bearing a 6′-substituent was initially believed to proceed through an epoxide intermediate, giving aurones or benzofuran-3(2H)-one derivatives as the chief reaction products. This was disputed when it was observed that AFO oxidation of (Z)-2′-hydroxy-α,4′,6′-trimethoxychalcone gave the erythro-α-methoxybenzofuran-3-one 7 (Scheme 3) instead of the threo-isomer, which is expected if an epoxide were an intermediate. Evidence to suggest that an epoxide can be an intermediate in this reaction when 2′-hydroxy-6′-substituted substrates are employed, is described herein.

Asymmetric synthesis of anti-(2S,3S)- and syn-(2R,3S)-diaminobutanoic acid

Conjugate addition of homochiral lithium N-benzyl-N-alpha-methylbenzylamide to tert-butyl (E)-cinnamate or tert-butyl (E)-crotonate and in situ amination with trisyl azide results in the exclusive formation of the corresponding 2-diazo-3-amino esters in > 95% de. Amination of the lithium (E)-enolates of tert-butyl (3S,alphaR)-3-N-benzyl-N-alpha-methylbenzylamino-3-phenylpropanoate or tert-butyl (3S,alphaS)-3-N-benzyl-N-alpha-methylbenzylaminobutanoate with trisyl azide gives the (2R,3R,alphaR)- and (2S,3S,alphaS )-anti-2-azido-3-amino esters in good yields and in 85% de and > 95% de respectively. Alternatively, tert-butyl anti-(2S,3S,alphaS)-2-hydroxy-3-N-benzyl-N-alpha-methylbenzylaminobutanoate may be converted selectively to tert-butyl anti-(2S,3S,alphaS)-2-azido-3-N-benzyl-N-alpha-methylbenzylaminobutanoate by aziridinium ion formation and regioselective opening with azide. Deprotection of tert-butyl (2S,3S,alphaS)-2-azido-3-aminobutanoate via Staudinger reduction, hydrogenolysis and ester hydrolysis furnishes anti-(2S,3S)-diaminobutanoic acid in 98%, de and 98% ee. The asymmetric synthesis of the diastereomeric syn-(2R,3S)-diaminobutanoic acid (98% de and 98% ee) was accomplished via functional group manipulation of tert-butyl anti-(2S,3S,alphaS)-2-hydroxy-3-N-benzyl-N-alpha-methylbenzylaminobutanoate in a protocol involving azide inversion of tert-butyl (2S,3S)-2-mesyloxy-3-N-Boc-butanoate and subsequent deprotection.

Development of a selective sorbent for the solid-phase extraction of terbuthylazine in olive oil samples: A molecular imprinting strategy

Aiming to implement an analytical methodology that is highly selective for the extraction and quantification of terbuthylazine from olive oil, we successfully achieved: (i) the development of a molecularly imprinted polymer by bulk polymerization using terbuthylazine as template molecule, methacrylic acid as functional monomer, ethylene glycol dimethacrylate as cross-linker, and dichloromethane as porogen; (ii) characterization of the imprinting material using Fourier transform infrared spectroscopy, thermogravimetric analysis, nitrogen adsorption at 77 K, and scanning electron microscopy; (iii) their molecular recognition for the template molecule using high-performance liquid chromatography, and (iv) optimization of a solid-phase extraction procedure using as sorbent the synthesized molecularly imprinted polymer for the selective extraction and clean-up of terbuthylazine from spiked organic olive oil and further quantification of the pesticide levels by high-performance liquid chromatography. The suitability of the implemented analytical methodology was demonstrated, as concentrations of terbuthylazine below the tolerated maximum residue limits in the spiked organic olive oil samples could be satisfactorily analyzed with good precision/accuracy with high recovery rates (96%). Overall, the implemented methodology has proven to be reliable and robust and is highly promising in the field of sample preparation, particularly for the isolation/preconcentration of terbuthylazine in complex food samples.

The alkylation of a novel acetal derived from (2R,3R)-(+)-tartaric acid: An unexpected rearrangement

Abstract The novel chiral bis -acetal dioxane 2a derived from (2 R ,3 R )-(+)-tartaric acid was shown to undergo an unexpected rearrangement upon treatment with lithium amide base to give the chiral dioxolane 3a in optically active form. Alkylation and aldol studies were performed on the diisopropyl ester of this dioxolane 3b .

Flavonoid epoxides. Part 20. Some unusual reactions of dimethyldioxirane (DMD) with flavonoid compounds

Abstract Dimethyldioxirane (DMD), generally as a solution in acetone, has proved itself to be an excellent epoxidising agent. It was observed that either the 2′-hydroxychalcone epoxide or the trans-2,3-dihydroflavonol could be obtained depending on the pH of the reaction mixture and the type of β-arene ring present in the substrate. Using this methodology trans-2,3-dihydroflavonols can be synthesised in far better yields than by the most commonly used method for their synthesis, that of the Algar-Flynn-Oyamada reaction. Treatment of both flavonol 14 and the novel isoaurone 21 with DMD gave unusual products instead of the expected epoxides, but nonetheless, an epoxide was assumed to have formed during the reaction.