Biotransformations of aromatic aldehydes by acetogenic bacteria

Vanillin was subject to O demethylation and supported growth of Clostridium formicoaceticum and Clostridium thermoaceticum. Vanillin was also stimulatory to the CO-dependent growth of Peptostreptococcus productus. The aldehyde substituent of vanillin was metabolized by routes which were dependent upon both the acetogen and a co-metabolizable substrate (e.g. carbon monoxide [CO]). C. formicoaceticum and C. thermoaceticum oxidized the aldehyde group of vanillin to the carboxyl level, while P. productus reduced the aldehyde group of vanillin to the alcohol level. In contrast, during CO-dependent growth, C. thermoaceticum reduced 4-hydroxybenzaldehyde to 4-hydroxybenzyl alcohol while P. productus both reduced and oxidized 4-hydroxybenzaldehyde to 4-hydroxybenzyl alcohol and 4-hydroxybenzoate, respectively. These metabolic potentials indicate aromatic aldehydes may affect the flow of reductant during acetogenesis.     

Oxidation of aromatic aldehydes by Serratia marcescens

Cell suspensions of Serratia marcescens catalyzed the oxidation of aromatic aldehydes into the corresponding acids in high yield under mild conditions.     

Oxovanadium(IV) complexes with aromatic aldehydes

The synthesis, structure and spectroscopic properties of complexes with the formula [V(IV)O(dsal)2(H2O)], where Hdsal = salicylaldehyde, o-vanillin and 3-ethoxysalicylaldehyde, are presented. The crystal and molecular structures of [V(IV)O(o-van)2(H2O)] (1) (o-Hvan = o-vanillin = 3-methoxysalicylaldehyde) is studied by single-crystal X-ray diffraction. Each molecule exhibits an octahedral geometry with the two o-van ligands coordinated cis to the V(IV)O2+ group. 1 is the first example of a structurally characterized vanadium complex involving O(aldehyde) as the donor atom and this enables a comparison between the bonding characteristics and the contributions of O(aldehyde), O(amide), O(carboxylate) and O(ketone) (in acetylacetone) to the parallel hyperfine coupling constant in VOL2 complexes.     

Cyclodextrin-aided microbial transformation of aromatic aldehydes by Saccharomyces cerevisiae

Summary Biotransformation of benzaldehyde and vanillin by growing cells of Saccharomyces cerevisiae was performed in an aqueous medium containing either - or -cyclodextrin at the same molar concentration as the substrate. The yeast fermentative activity, as reflected by CO₂ evolution, and bioconversion to the corresponding alcohols were both faster and greater in the presence of the cyclic dextrins. Clearly, cyclodextrins were shown to significantly alleviate the inhibitory effects of the aromatic aldehydes.     

Generation of electronically excited aromatic aldehydes in the peroxidase catalyzed aerobic oxidation of aromatic acetaldehydes

The peroxidase catalyzed aerobic oxidation of aromatic acetaldehydes has been investigated with regard to the formation of electronically excited states because it generates the products expected from the cleavage of an intermediate dioxetane, that is, the aromatic aldehyde and formic acid. Emission was detected with the liquid scintillation counter. Integrated emission, indole-3-aldehyde formation, and O₂ uptake strictly correlate with each other, unequivocally indicating that the aromatic aldehyde is generated electronically excited. Although the quantum yield of emission is approximately 5×10^?9, the yield of chemiexcitation must be several orders of magnitude higher.     

New inhibitors of aldose reductase: anti-oximes of aromatic aldehydes

Aldose reductase is an NADPH-dependent enzyme which catalyzes the reduction of glucose to sorbitol. Specific potent inhibitors of aldose reductase are of potential pharmacological use because elevated levels of sorbitol produced by this enzyme in lens, peripheral nerve, retina, and renal glomeruli may be responsible for the pathogenesis associated with chronic diabetes. These inhibitors could also serve as probes of the mechanism of action of aldose reductase. anti-Oximes of aromatic aldehydes (e.g., benzaldoxime and 4-fluorobenzaldoxime) have proved to be effective inhibitors of aldose reductase rivaling pharmacological agents currently used to inhibit this enzyme in vivo. The kinetic patterns of inhibition in which benzyl alcohol is used as the oxidizable substrate suggest that the inhibition is due to the formation of a stable ternary complex composed of aldose reductase, NADP+, and the anti-oxime. Analogus ternary complexes are formed at the active site of horse liver alcohol dehydrogenase which is also inhibited by anti-oximes of efficient substrates.     

Metabolism of aromatic aldehydes as cosubstrates by the acetogen Clostridium formicoaceticum

When the acetogen Clostridium formicoaceticum was cultivated on mixtures of aromatic compounds (e.g., 4-hydroxybenzaldehyde plus vanillate), the oxidation of aromatic aldehyde groups occurred more rapidly than did O-demethylation. Likewise, when fructose and 4-hydroxybenzaldehyde were simultaneously provided as growth substrates, fructose was utilized only after the aromatic aldehyde group was oxidized to the carboxyl level. Aromatic aldehyde oxidoreductase activity was constitutive (activities approximated 0.8 U mg^–1), and when pulses of 4-hydroxybenzaldehyde were added during fructose-dependent growth, the rate at which fructose was utilized decreased until 4-hydroxybenzaldehyde was consumed. Although 4-hydroxybenzaldehyde inhibited the capacity of cells to metabolize fructose, lactate or gluconate were consumed simultaneously with 4-hydroxybenzaldehyde, and lactate or aromatic compounds lacking an aldehyde group were utilized concomitantly with fructose. These results demonstrate that (1) aromatic aldehydes can be utilized as cosubstrates and have negative effects on the homoacetogenic utilization of fructose by C. formicoaceticum, and (2) the consumption of certain substrates by this acetogen is not subject to catabolite repression by fructose. Received: 14 May 1998 / Accepted: 7 August 1998     

Biotransformation of aromatic aldehydes bySaccharomyces cerevisiae: Investigation of reaction rates

Summary The rate of production ofl-phenylacetyl carbinol bySaccharomyces cerevisiae in reaction mixtures containing benzaldehyde with sucrose or pyruvate as cosubstrate was investigated in short 1 h incubations. The effect of yeast dose rate, sucrose and benzaldehyde concentration and pH on the rate of reaction was determined. Maximum biotransformation rates were obtained with concentrations of benzaldehyde, sucrose and yeast of 6 g, 40 g and 60 g/l, respectively. Negligible biotransformation rates were observed at a concentration of 8 g/l benzaldehyde. The reaction had a pH optimum of 4.0–4.5. Rates of bioconversion of benzaldehyde and selected substituted aromatic aldehydes using both sucrose and sodium pyruvate as cosubstrate were compared. The rate of aromatic alcohol production was much higher when sucrose was used rather than pyruvate.o-Tolualdehyde and 1-chlorobenzaldehyde were poor substrates for aromatic carbinol formation although the latter produced significant aromatic alcohol in sucrose-containing media. Yields of 2.74 and 3.80 g/l phenylacetyl carbinol were produced from sucrose and pyruvate, respectively, in a 1 h reaction period.     

Bidirectional transformation of aromatic aldehydes by Desulfovibrio desulfuricans under nitrate-dissimilating conditions

M. PAREKH, H.L. DRAKE AND S.L. DANIEL 1996. Desulfovibrio desulfuricans ATCC 27774 was screened for reactivity against aromatic compounds during lactate-dependent, nitrate-dissimilating growth. Only aromatic aldehydes (benzaldehyde, 2-hydroxybenzaldehyde, 3-hydroxybenzaldehyde, 4-hydroxybenzaldehyde, vanillin, iso -vanillin and o -vanillin) were reactive and, with the exception of 2-hydroxybenzaldehyde, were stimulatory to lactate-dependent growth. Aromatic aldehydes were transformed to their corresponding benzoate and benzyl alcohol derivatives, with the ratio of benzoate-to-benzyl alcohol derivatives being dependent upon lactate availability. In presence of lactate, aromatic aldehydes were primarily reduced to their corresponding benzyl alcohol derivatives; in the absence of lactate, aromatic aldehydes were mainly oxidized to their corresponding benzoate derivatives. In the absence of nitrate, 3-hydroxybenzaldehyde was neither reduced nor oxidized. These results indicate that D. desulfuricans is competent in the bidirectional transformation of aromatic aldehydes under nitrate-dissimilating conditions and that the direction of transformation (i.e. reduction or oxidation) is regulated by reductant availability.     

Plants as a green alternative for alcohol preparation from aromatic aldehydes

A general methodology for the efficient reduction of aromatic aldehydes and three ketones to their corresponding alcohols (interesting as cosmetic fragrances in their majority) with moderate to excellent chemical yield was achieved by using homogenates of broccoli (B. oleracea var. italic), cauliflower (B. oleracea var. botrytis), beet (B. vulgaris var. cicla), and spinach (S. oleraceae) in aqueous suspension and mild reaction conditions. B. oleracea var. italic and B. oleracea var. botrytis gave the maximum bioconversion yields within short reaction times. Vegetables assayed exhibited an excellent yield (≥ 99%) after 24 hours for aromatic aldehydes.     

A new dehydrogenase specific towards aromatic aldehydes from a halophilic bacterium

A new enzyme showing a dehydrogenase activity towards aromatic aldehydes was isolated, purified and characterized from a halophilic strain isolated from saline environment. The enzyme is a monomer of 54 kDa; it is rather thermostable (optimal temperature: 50 degrees C) showing a broad spectrum of activity in a large pH range with the maximum at pH 9.5. The substrate specificity and the effect of ions were evaluated and compared with analogous described proteins.     

Racemization of amino acid esters by aromatic aldehydes in basic non-aqueous solvents

Summary Aromatic aldehydes catalyze the racemization of amino acid esters dissolved in organic solvents. The racemization rate depends on the kind of aldehyde and is sensitive to general base catalysis. Active aldehydes bound to an insoluble support racemize amino acid esters in a heterogeneous phase system. Several aspects of the mechanism, together with possible applications of this reaction to the resolution of racemic mixtures of amino acids, are discussed.     

Purification and properties of reductases for aromatic aldehydes and ketones from guinea pig liver.

NADPH-dependent enzymatic reduction of aromatic aldehydes and ketones observed in the cytosol of guinea pig liver was mediated by at least three distinct reductases (AR 1, AR 2, and AR 3), which were separated by DEAE-cellulose chromatography. By several procedures AR 2 and AR 3 were purified to homogeneity, but AR 1 could be purified only 30-fold because of the small amount. These enzymes were found to have similar molecular weights of 34,000 to 36,000 and similar Stokes radii of about 2.5 nm. AR 3 was identical to aldehyde reductase [EC 1.1.1.2] in substrate specificity for aromatic aldehydes and D-glucuronate and specific inhibition by barbiturates. AR 1 and AR 2 acted on aromatic ketones and cyclohexanone as well as aromatic aldehydes at optimal pHs of 5.4 and 6.0, respectively, and were immunochemically distinguished from AR 3. AR 1 was the most sensitive to sulfhydryl reagents, and AR 2 was more stable at 50 degrees C than the other enzymes. Similar heterogeneity was observed in the kidney enzymes, but other tissues had little aldehyde reductase activity and contained only AR 3. In addition, lung contained a high molecular weight aromatic ketone reductase different from the above reductases.     

Chiral aminonaphthol-catalyzed enantioselective carbonyl addition of diethylzinc to aromatic aldehydes high-throughput screened by CD-HPLC analysis

Optically active aminonaphthols derivatives are obtained by condensation of 2-naphthol, substituted benzaldehyde, and (S)-methylbenzylamine under mild conditions, without side products. Their absolute configurations are determined by X-ray crystallographic analysis. The addition of diethylzinc to aromatic aldehydes is considerably accelerated by the presence of a catalytic amount of crystalline to give, after hydrolysis, the corresponding 1-phenylpropanol in good enantiomeric purity, as determined by CD-HPLC analysis as HTPS (high-throughput screening).     

Structural influence of chiral tertiary aminonaphthol ligands on the asymmetric phenyl transfer to aromatic aldehydes

A series of chiral tertiary aminonaphthol ligands were prepared from 2-naphthol, (S)-1-phenylethylamine, and aldehydes with diverse substituted groups. The results of asymmetric phenyl transfer to aromatic aldehydes catalyzed by these chiral ligands indicated that enantioselectivities were greatly influenced by the electronic and steric effects of the ligands.     

Characterization of Sphingomonas aldehyde dehydrogenase catalyzing the conversion of various aromatic aldehydes to their carboxylic acids

Natural products represent an important source of drugs in a number of therapeutic fields, e.g. antiinfectives and cancer therapy. Natural products are considered as biologically validated lead structures, and evolution of compounds with novel or enhanced biological properties is expected from the generation of structural diversity in natural product libraries. However, natural products are often structurally complex, thus precluding reasonable synthetic access for further structure-activity relationship studies. As a consequence, natural product research involves semisynthetic or biotechnological approaches. Among the latter are mutasynthesis (also known as mutational biosynthesis) and precursor-directed biosynthesis, which are based on the cellular uptake and incorporation into complex antibiotics of relatively simple biosynthetic building blocks. This appealing idea, which has been applied almost exclusively to bacteria and fungi as producing organisms, elegantly circumvents labourious total chemical synthesis approaches and exploits the biosynthetic machinery of the microorganism. The recent revitalization of mutasynthesis is based on advancements in both chemical syntheses and molecular biology, which have provided a broader available substrate range combined with the generation of directed biosynthesis mutants. As an important tool in supporting combinatorial biosynthesis, mutasynthesis will further impact the future development of novel secondary metabolite structures.     

Bioreduction of aromatic aldehydes and ketones by fruits’ barks of Passiflora edulis

A series of ketones and aldehydes were reduced using plant cell preparations from fruits’ barks of Passiflora edulis in water as solvent. The reduced products were obtained in very good yields, and low to moderate enantiomeric excesses were reached with aromatic ketones and a β-ketoester. This is the first time that the biotransformation of carbonyl compounds have been successfully achieved using Passiflora species.     

Chemienergized aromatic aldehydes from the peroxidase catalyzed oxidation of pyruvates: excited vanillin from vanylpyruvate.

Oxidation by molecular oxygen of vanylpyruvate in dimethylsulfoxide containing potassium t-butoxide results in formation of emissive, electronically excited (singlet) vanillin and of oxalate, that is, the products expected from the cleavage of a dioxetane intermediate. The reaction is a model for the peroxidase and laccase catalyzed processes that occur during lignin degradation by fungi. It is inferred that vanillin formed in the latter processes is generated in an electronically excited state, not necessarily emissive. This view is strengthened by (i) the emission, albeit very weak, observed from the enzyme system, and (ii) the alteration of the enzyme as a result of the reaction, the spectral changes being similar to those induced by uv irradiation of the enzyme alone. Also other peroxidase catalyzed oxidations of aromatic pyruvates should produce the electronically excited aldehyde.