Effect of borohydride reduction on antibodies

The effect of borohydride reducing reagents on monoclonal and polyclonal antibodies was examined by enzyme-linked immunosorbent assay (ELISA). Each antibody showed different stability characteristics to the reducing reagents. Sodium cyanoborohydride was at least five times milder toward immunological activity than sodium borohydride, however, sodium cyanoborohydride with a catalytic amount of metal ion (Zn²⁺ or Al³⁺ ) can be as harsh as sodium borohydride. Activated hydrophobic borohydrides, 9BBN-pyridine, did not have any advantages in respect to the stabilities of antibodies. Antibodies to be used for immunosorbent purification must be evaluated individually to determine whether their structure is stable to immobilization reagents and conditions prior to their linkage to the column support.     

Altered selectivity of reduction of steroidal carbonyls

The reduction of steroidal ketones in different solvents yielded different products. These conditions which altered the normal path, yielded a selective reduction of the Δ⁴-3 carbonyl without the concomitant reduction of the C-17 or C-20 ketones; this permitted a one step partial synthesis of 3β-hydroxy-Δ⁴-pregnen-20-one (I), 3β-hydroxy-5-pregnan-20-one (II), and of 3β,11β-dihydroxyandrostan-17-one (IV).     

Catalytic enantioselective borohydride reduction of ortho-fluorinated benzophenones

[reaction: see text] In the presence of the optically active ketoiminatocobalt(II) complexes, the enantioselective borohydride reduction of benzophenones was successfully completed. The fluorine atom on the ortho position of the benzophenone and aryl ketones proved effective for obtaining high enantioselectivities. The combined use of modified lithium borohydride afforded the corresponding benzhydrols and arylcarbinols in high yield and high enantioselectivity (88-96% ee).     

Chemoselective reduction of aldehydes with zinc borohydride in tetrahydrofuran

A variety of structurally different aldehydes undergo chemoselectire reduction over ketones with zinc borohydride in tetrahydrofuran at −10°C to the corresponding alcohols.     

Ruthenium catalysed reduction of alkenes using sodium borohydride

The reduction of alkenes has been achieved using NaBH₄ as the reducing agent using 0.5-1.0 mol % Ru(PPh₃)₄H₂ in the presence of water.     

Heterocycles. XXV Sodium borohydride reduction of flavanonols

Solvent effects on the stereochemistry in the sodium borohydride reduction of (±)-flavanonols have been examined. The effects observed for the (±)-flavanonols with 5-OMe in 2-propanol, dioxane and methanol are explainable by the differences between the steric interactions inherent in the product-like transition states A and B. It has been also found that 5-OAc peculiarly affects the stereochemistry in the reduction to produce the (±)-catechin-type compounds in a one-pot process. The solvent and temperature effects are examined using a model analogous to the above.     

Selective reduction of vinylhydroxyphenyl azomethines by sodium borohydride

Conclusions Vinylhydroxyphenyl azomethines are reduced by sodium borohydride at room temperature only at the azomethine group.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 9, pp. 2076–2078, September, 1978.     

Photo-enhanced reduction of carbonyl compounds by sodium borohydride

The reduction of ketones and some esters by sodium borohydride is dramatically accelerated by uv irradiation. The reaction seems to proceed from the (n, π) excited state of the carbonyl compound. The photocatalytic effect is dependent on the solvent polarity and substituents on aromatic carboxylic acids and alcohols of esters.     

Observations on the reduction of aryl nitro groups with palladium-sodium borohydride

The reduction of aryl nitro groups by the palladium-sodium borohydride system can be controlled in some instances to give products differing from those of catalytic hydrogenation. With six equivalents of borohydride added to the catalyst 2,2′-dinitrobiphenyl formed only 2,2′-diaminobiphenyl. With added sodium hydroxide and varying amounts of borohydride and catalyst, the reduction can be controlled to give benzo[c]cinnoline, benzo[c]cinnoline 5-oxide or benzo[c]cinnoline 5,6-dioxide. In a closed system, the reagents reduce both the nitro and olefin functional groups in 6-nitro-5,8-dimethoxy-1,4-dihydro-1,4-ethano-naphthalene. In an open flask flushed with argon, the reduction is confirmed to the nitro group. Reduction of 2-chloro and 4-chloronitrobenzene with palladium-borohydride gives substantial yields of the appropriate chloroanilines. In contrast, hydrogen and palladium give aniline as the major product from each of these. These results suggest that the addition of sodium borohydride to palladium on carbon produces a reductive entity differing from that of catalytic hydrogenation.     

The mechanism of aluminum-catalyzed Meerwein-Schmidt-Ponndorf-Verley reduction of carbonyls to alcohols

The mechanistic details of the Meerwein-Schmidt-Ponndorf-Verley (MSPV) reduction of ketones to the corresponding alcohols were investigated both experimentally and computationally. Density functional theory (DFT) was used to assess the energetics of several proposed pathways (direct hydrogen transfer, hydridic, and radical). Our results demonstrate that a direct hydrogen transfer mechanism involving a concerted six-membered ring transition state is the most favorable pathway for all calculated systems starting from a small model system and concluding with the experimentally investigated BINOLate/Al/(i)PrOH/MePhC=O system. Experimental values for the activation parameters of acetophenone reduction using the BINOLate/Al/(i)PrOH system (DeltaG# = 21.8 kcal/mol, DeltaH# = 18.5 kcal/mol, DeltaS# = -11.7 au) were determined on the basis of kinetic investigation of the reaction and are in good agreement with the computational findings for this system. Calculated and experimental kinetic isotope effects support the concerted mechanism.     

The synthesis and borohydride reduction of some alloxazine derivatives

Unequivocal syntheses of N(1 or 3)-mono-substituted 7, 8-dimethylalloxazines are described. The borohydride reduction of various alloxazines has been studied under aerobic and anaerobic conditions, in the absence of light. These reactions are discussed in relation to other work on 7, 8-dimethylisoalloxazines (flavins) and on certain flavoproteins.     

A computer study of borohydride reduction kinetics and stereochemistry

A computer simulation of the sodium borohydride reduction of an alkyl-substituted cyclohexanone in isopropanol has shown the following two apparently contradictory experimental observations to be compatible: (1) The kinetics are experimentally indistinguishable from second-order, with the first hydride transfer rate determining. (2) The cis : trans product ratio changes significantly during the course of reduction. The calculations suggest that the fourth hydride transfer is the second-slowest, with a rate constant approximately eight times that of the first.     

Investigations of polyaniline-platinum composites prepared by sodium borohydride reduction

Two procedures were applied for the preparation of polyaniline (PANI)-Pt composites in aqueous solutions using sodium borohydride as the reducing agent. The first one involved reduction of Pt ions originating from PtCl₄ conducted in the presence of PANI. The second was a two-step method in which doping of PANI with Pt-containing anions was followed by their reduction. The composites containing various amounts of Pt were obtained. They were characterized by X-ray diffraction, X-ray photoelectron and IR spectroscopies. This allowed to establish differences in the efficiency of both methods of composite preparation. It was also found that the composites show mainly redox activity in catalytic isopropyl alcohol conversion.     

Enantioselective borohydride reduction catalyzed by optically active cobalt complexes

The highly enantioselective borohydride reduction of aromatic ketones or imines to the corresponding alcohols was developed in the presence of a catalytic amount of an optically active cobalt(II) complex catalyst. This enantioselective reduction is carried out using a precisely premodified borohydride with alcohols such as tetrahydrofurfuryl alcohol, ethanol and methanol. High optical yields are obtained by choosing the appropriate alcohol as modifiers and a suitable beta-ketoiminato ligand of the catalyst. The enantioselective borohydride reduction has been successfully applied to the preparation of optically active 1,3-diols, the stereoselective reduction of diacylferrocenes, and dynamic and/or kinetic resolution of 1,3-dicarbonyl compounds.     

Multidimensional chromatographic separation of estrogen receptors

Analyses of estrogen and progesterone receptors in biopsies of breast carcinoma play a vital role in the selection of patients likely to respond to hormone manipulation. Sucrose density gradient centrifugation has been the reference method in the determination of estrogen receptors in human breast carcinoma cytosols. To reduce assay time and circumvent prolonged manipulation of labile receptor preparations, high performance liquid chromatography techniques in the size-exclusion and ion-exchange modes were compared as potential alternate methods for the rapid separation of receptor isoforms. Multidimensional analyses were performed by reapplying estrogen receptor isoforms obtained from high performance size-exclusion and ion-exchange chromatography to sucrose density gradients and vice versa. This confirmed that the estrogen-binding components identified by high performance liquid chromatography appear to correspond to estrogen receptor species from sucrose density gradients.