F. C. Alderweireldt

Enzymatic in vitro reduction of ketones: 15. The influence of reaction conditions on the stereochemical course of HLAD-catalyzed reductions: 3-Cyano-4,4-dimethylcyclohexanone as a sensitive probe

Abstract The stereochemical course of the horse liver alcohol dehydrogenase (HLAD)-catalyzed reduction is studied on substituted cyclohexanones under varying reaction conditions. Temperature, pH, and ethanol concentration influence the stereochemical course of the reduction of some substrates. Moreover, the quantitative aspects of the stereochemistry of HLAD-catalyzed reductions seem to vary with the origin of the enzyme preparations. 3-Cyano-4,4-dimethylcyclohexanone is an appropriate and sensitive test substrate in the study of these influences.

Enzymatic in vitro reduction of ketones. Part 2. Study of coenzyme recycling in an ethanol–cyclohexanone system with HLAD (Horse Liver Alcohol Dehydrogenase)

The coupled-substrate recycling system is elaborated for a reaction mixture containing cyclohexanone–ethanol (as coupled substrate), the co-enzyme NAD+, and the enzyme HLAD. All reaction parameters are discussed in order to optimize the reduction of cyclohexanone as a model compound for other reductions, mainly to synthesize chiral compounds. With catalytic amounts of co-enzyme 50 000 recyclings could be realized. A formula for the initial rate of the enzymatic reaction based on a double Theorell–Chance mechanism is given and experimentally checked.

Enzymatic in vitro reduction of ketones. Part 8. A new model for the reduction of cyclic ketones by horse liver alcohol dehydrogenase. (HLAD)

The values for the reaction rate constants of the catalytic step HLAD-NADH + ketone → HLAD-NAD++ alcohol in the HLAD-catalysed reduction of cyclic ketones are rationalized in a new model. The fundamental concepts of the model are discussed. An extensive description of the model-building is presented and its predictive value for any possible six-membered ring substrate is shown. A comparison with previous models is given.

Synthesis and biological evaluation of 4-carbamoyl-2-β-D-ribofuranosyl-pyridine

Abstract D-Allo/D-altro 2-(2,4:3, 5-di-O-benzylidenepentitol-1-y1)-4-(4,4-dimethyloxazolin-2-y1)pyridine was synthesized from 2-lithio-4-(4,4-dimethyloxazolin-2-y1)pyridine and 2, 4:3,5-di-O-benzylidenealdehydo-D-ribose. After mesylation and subsequent treatment of the adduct with CF3COOH/H2O and then ammonia, 4-carbamoyl-2-D-ribofuranosylpyridine was formed. The α- and β-anomers were separated by semipreparative hplc on a LICHROSORB 10 DIOL column. The β-anomer had no antiviral activity, but it had modest cytostatic activity against tumor cells.

Synthesis and biological evaluation of some D-xylofuranosyl-pyridine C-nucleosides

Abstract The addition reaction of either 3-bromo-5-lithiopyridine (2a) or 3-cyano-5-lithiopyridine (2b) to 2,4:3,5-di-O-benzylidene-aldehydo-D-xylose (1) gave a D-gulo/D-ido mixture of respectively 3-bromo- and 3-cyano-5-(2,4;3,5-di-O-benzylidene-pentitol-1-yl)pyridine (3a, b). Mesylation of C-1′ followed by reaction with CF3COOH/H2O resulted in the formation of the corresponding D-xylo-furanosyl pyridine C-nucleosides. 3-Cyano-5-D-xylofuranosylpyridine (5b) was converted to 3-carbamoyl-5-D-xylofuranosylpyridine (6) with Amberlite IRA 400 (OH−). The D-xylofuranosyl C-nucleosides were evaluated for their antiviral and cytostatic activity. No significant activity was found.

Ring-size effects in horse liver alcohol dehydrogenase-catalyzed redox reactions

Abstract For the four- to the nine-membered cycloalkanone-cycloalkanol pairs, the equilibria, reduction rates, and oxidation rates of the horse liver alcohol dehydrogenase (HLAD)-catalyzed redox reaction are determined. Depending on the ring size, the equilibria lie more or less extremely to the cycloalkanone side. The equilibria and the reduction rates of the cycloalkanones show the same characteristic dependence on the ring-strain differences between ketones and alcohols. The oxidation rates do not show this dependence which only increase for increasing ring sizes. The conclusion is that two main effects control the rates of HLAD-catalyzed redox reactions on cyclic substrates: ring-strain differences between the substrate and a cycloalkanol-like transition state, and hydrophobic interactions between the substrates and a hydrophobic substrate-binding pocket.

Synthesis and Biological Evaluation of 3-Chloro-4-(D-Ribofuranosyl)-Pyridine and 3-(D-Ribofuranosyl)-2- Pyridone

Abstract Condensation of 2-fluoro-3-lithio pyridine and 3-chloro-4-lithio pyridine with 2,4:3,5-di-O-benzylidene-alde-hydo-D-ribose gives the corresponding D-allo- and D-altro-addition products. These were converted into the corresponding mesylates and cyclized to the ribofuranosyl nucleosides with an overall yield of 60–70 %. Both nucleosides did not show any inhibitory effect on L-1210-cells.

HPLC and LC-MS of Nucleosides

Abstract An LC-MS system for the analysis and unambigious identification of nucleosides is described using a microbore column and volatile buffer systems. The detection of pseudouridine in normal urine was used as a test for diagnostic applications.

Stereospecific synthesis of a novel series of pyridine nucleosides

Abstract Condensation of 3,5- di -O- benzoyl -β- d - ribofuranosyl chloride severally with 3-acetyl-5-alkylpyridines, 5-alkyl-3-methoxycarbonylpyridines (alkyl = Me, Et, Pr, and i Pr), 5-isopropylnicotinamide, and 3,5-diacetylpyridine bis(ethylene acetal) in acetonitrile at −5° gave the corresponding 1-(3,5- di -O- benzoyl -β- d - ribofuranosyl ))-3,5- disubstituted pyridinium chlorides in excellent yield (90%). From the reaction of a series of 2,3-O- isopropylidene -β- d -ribofuranosyl halides with 3-acetyl-5-methyl-pyridine at room temperature, the α -nucleosides were obtained.

Analysis of Substituted Pyridine-C-Nucleosides by Direct Liquid Introduction Liquid Chromatography/Mass Spectrometry

Abstract A method was elaborated for the analysis of a few original pyridine-C-nucleosides via microbore DLI/LC-MS. The compounds were analyzed on a 10RP8 column (25 cm × 1 mm) using a number of 0.01 M HCOONH4/CH3OH mixtures as eluant. Under appropriate LC-MS conditions, both α- and β-anomers were separated and identified. All nucleosides were characterized by the protonated molecular ion [MH]+, [B+30]+ and [B+44]+-fragment ions. Assignment of the α, β-configuration at C1′ was done with the aid of 13C-NMR. From the DLI/LC-MS data, a semi-preparative HPLC-method was developed to purify the pyridine-C-nucleosides prior to biological evaluation.