A Light-Activated Antibody Catalyst

Unusually Chemoselective Photocyclization of 2-(Hydroxyimino)aldehydes to Cyclobutanol Oximes: Synthetic, Stereochemical, and Mechanistic Aspects

Photocyclization of carbonyl compounds (known as the Norrish-Yang reaction) to yield cyclobutanols is, in general, accompanied by fragmentation reactions. The latter are predominant in the case of aldehydes so that secondary cyclobutanols are not considered accessible via the straightforward Norrish-Yang reaction. A noteworthy exception has been reported in our laboratory, where cyclobutanols bearing a secondary alcohol function were observed upon UV light irradiation of 2-(hydroxyimino)aldehydes (HIAs). This reaction is here investigated in detail by combining synthesis, spectroscopic data, molecular dynamics, and DFT calculations. The synthetic methodology is generally applicable to a series of HIAs, affording the corresponding cyclobutanol oximes (CBOs) chemoselectively (i.e., without sizable fragmentation side-reactions), diastereoselectively (up to >99:1), and in good to excellent yields (up to 95%). CBO oxime ether derivatives can be purified and diastereomers isolated by standard column chromatography. The mechanistic and stereochemical picture of this photocyclization reaction, as well as of the postcyclization E/Z isomerization of the oxime double bond is completed.

Thienyl-Substituted α-Ketoamide: A Less Hydrophobic Reactive Group for Photo-Affinity Labeling

Photoaffinity labeling (PAL) is an important tool in chemical biology research, but application of α-ketoamides for PAL has been hampered by their photoinstability. Here, we show that 2-thienyl-substituted α-ketoamide is a superior photoreactive group for PAL. Studies with a series of synthetic mannose-conjugated α-ketoamides revealed that 2-thienyl substitution of α-ketoamide decreased the electrophilicity of the keto group and reduced the rate of photodegradation. Mannose-conjugated thienyl α-ketoamide showed greater concanavalin A labeling efficiency than other alkyl or phenyl-substituted α-ketoamides. In comparison with representative conventional photoreactive groups, 2-thienyl ketoamide showed reduced labeling of nontarget proteins, probably owing to its lower hydrophobicity.

The syntheses of α-ketoamides vianBu4NI-catalyzed multiple sp3C–H bond oxidation of ethylarenes and sequential coupling with dialkylformamides

The ⁿBu₄NI-catalyzed sequential C–O and C–N bond formation via multiple sp³C–H bond activation of ethylarenes, using N,N-dialkylformamide as the amino source, provided α-ketoamides with moderate yields.

Antibody-catalyzed oxidative degradation of nicotine using riboflavin

Tobacco abuse remains a major cause of death worldwide despite ample evidence linking nicotine to various disease states. Consequently, immunopharmacotherapeutic approaches for the treatment of nicotine abuse have received increasing attention. Although a number of nicotine-binding antibodies have been disclosed, no antibody catalysts exist which efficiently degrade nicotine into pharmacologically inactive substances. Herein, we report the first catalytic antibodies which can oxidatively degrade nicotine. These biocatalysts use the micronutrient riboflavin and visible light as a source of singlet oxygen for the production of reactive oxygen species. Along with various known nicotine metabolites, antibody-catalyzed nicotine oxidations produce two novel nicotine oxidation products that were also detected in control ozonation reactions of nicotine. The reaction is efficient, with multiple turnovers of catalyst observed and total consumption of nicotine attained. These results demonstrate the potential of harnessing riboflavin as an endogenous sensitizer for antibody-catalyzed oxidations and demonstrate a new approach for the development of an active vaccine for the treatment of nicotine addiction using in vivo catalytically active antibodies.

Origin of Selectivity in the Antibody 20F10-Catalyzed Yang Cyclization

The first antibody-catalyzed Yang (Norrish type II) cyclization has been achieved with antibodies that were elicited against cis- and trans-2,3-diaryloxetanes. The photocyclization of 1,4-diarylbutan-1-one produced a single stereoisomer of cis-1,2-diarylcyclobutanol with very high enantioselectivity. The background photochemical reaction in the absence of the antibody yielded only fragmentation products. The antibody 20F10-catalyzed reaction was studied in detail, exploring its selectivity, substituent effects, substrate and hapten binding, kinetic parameters and irradiation wavelength dependence. Quantum mechanical calculations suggest that the activation enthalpy of fragmentation pathway is favored by 7.9 kcal/mol over cyclization pathway. Hapten, substrate, and transition state docking studies on a homology based modeled antibody binding site indicate that the trans hapten, substrate and the cyclization transition state have similar binding modes. By contrast, the fragmentation transition state is bound in a different way, not easily accessible within the lifetime of the bound substrate excited state. Several side chain residues were identified that can act as local sensitizers to enhance the cyclization process.

Catalysis of the Photo-Fries Reaction: Antibody-Mediated Stabilization of High Energy States

A conformationally constrained hapten is presented that is capable of catalyzing the first antibody-mediated photo-Fries rearrangement. In this reaction, absorption of light energy by a diphenyl ether substrate results in homolytic C-O bond cleavage followed by recombination to yield biphenyl-derived products. The most proficient antibody studied converts 4-phenoxyaniline 15 into 2-hydroxy-5-aminobiphenyl 16 under high-intensity irradiation at a rate of 8.6 microM/min. These results support a recent hypothesis stating that immunization with conformationally constrained haptens provides higher titers for the acquisition of simple binding antibodies; however, in this case, conformational constraint does not ensure the development of more efficient catalysts. Using the obtained antibodies, the presence of products resulting from escape of free radicals from the solvent cage can be suppressed, altering the excited state energy surface such that free radicals are funneled into the formation of the desired biphenyl product. However, studies also show the inactivation of the antibodies as a result of photodecay of the biphenyl product. Using an isocyanate scavenging resin, the photodecay product could be removed and the inactivation of the antibody drastically reduced. Furthermore, despite the observed photodecay, turnover of the antibody was present; this represents the first case in which true turnover of a photochemical reaction using a catalytic antibody could be observed.

Synthesis and SAR evaluation of oxadiazolopyrazines as selective Haemophilus influenzae antibacterial agents

The parallel synthesis and antibacterial activity of 5-hydroxy[1,2,5] oxadiazolo[3,4-b]pyrazines is reported. The compounds were synthesized by condensing diaminofurazan with alpha-keto acids to give a variety of aryl-substituted analogues. Halogenated phenyl groups at C-6 give rise to the greatest Haemophilus influenzae antibacterial activity.

Synthesis and biological activity of strongly fluorescent tricyclic analogues of acyclovir and ganciclovir

In search of strongly fluorescent tricyclic analogues of acyclovir (ACV, 1) and ganciclovir (GCV, 2), derivatives of the 3,9-dihydro-9-oxo-5H-imidazo[1,2-a]purine system, several 6-[4-(acyloxy)phenyl], 6-[4-(acylamino)phenyl], and 6-[4-(phenoxycarbonyloxy)phenyl]-substituted TACV and TGCV analogues were synthesized and evaluated for their activity against herpes simplex virus types 1 and 2 in cell culture. All TACV and TGCV analogues showed strong fluorescence (quantum yield of 30-65% vs 2-aminopurine 100%). The 6-[4-(phenoxycarbonyloxy)phenyl]-substituted compounds 11 and 19 displayed the best combination of the fluorescence and antiviral potency.

2-Aryl-2,2-difluoroacetamide FKBP12 ligands: synthesis and X-ray structural studies

[structure: see text] 2-Aryl-2,2-difluoroacetamido-proline and pipecolate esters are high affinity FKBP12 ligands whose rotamase inhibitory activity is comparable to that seen for the corresponding ketoamides. X-ray structural studies suggest that the fluorine atoms participate in discrete interactions with the Phe36 phenyl ring and the Tyr26 hydroxyl group, with the latter resembling a moderate-to-weak hydrogen bond.

Photoreactivation of alloxanthine-inhibited xanthine oxidase

Alloxanthine-inhibited xanthine oxidase (XOD) was found to be photoreactivated by irradiation of light of wavelengths in the range of 340-430 nm. The enzyme activity can be fully controlled to be on or off by many dark-light cycles. Electron spin resonance measurement shows the appearance of the molybdenum (V) ion and the reduced form of flavin adenine dinucleotide (FADH.) radical signals after irradiation of the alloxanthine-XOD complex. Electronic-absorption spectrum also shows the bleaching of Fe/S and flavin adenine dinucleotide chromophores at 375 and 450 nm as well as broad-band absorption of FADH. in the range of 500-700 nm. The quantum yield of photoreactivation of the enzyme activity is approximately 0.06. A photoinduced intraenzyme electron-transfer model is proposed to rationalize the photoreactivation process.

Alpha-ketoamides and alpha-ketocarbonyls: conformational analysis and development of all-atom OPLS force field

The molecular structures and barriers for the internal rotation around the OC-CO single bond in four alpha-ketoamides and eight alpha-ketocarbonyls have been determined from the MP3/aug-cc-pVDZ and MP2/aug-cc-pVDZ calculations. Alpha-ketocarbonyls with non-bulky substituents adopt planar conformations with two carbonyl oxygens in s-trans arrangement. The s-cis conformation is significantly less stable due to the electrostatic repulsion between the two carbonyl groups. Primary and secondary alpha-ketoamides are planar when the substituent at the carbonyl carbon is hydrogen or methyl group but tertiary alpha-ketoamides adopt a conformation where the OC-CO unit is significantly bent. Based on current ab initio structural data, a set of OPLS-AA force field parameters has been derived. These parameters can be used for the modeling of a variety of alpha-ketoamide or alpha-ketocarbonyl containing drugs such as novel protease inhibitors or neuroregenerative polyketides.