Lajos Novák

Optically active 1-(benzofuran-2-yl)ethanols and ethane-1,2-diols by enantiotopic selective bioreductions

Abstract Enantiotopic selective reduction of 1-(benzofuran-2-yl)ethanones 1a – d , 1-(benzofuran-2-yl)-2-hydroxyethanones 4a – c and 2-acetoxy-1-(benzofuran-2-yl)ethanones 3a – c was performed by bakers yeast for preparation of optically active (benzofuran-2-yl)carbinols [( S )- 5a – d , ( S )- 6a – c and ( R )- 6a – c , enantiomeric excess from 55 to 93% ee].

Baker's yeast mediated stereoselective biotransformation of 1-acetoxy-3-aryloxypropan-2-ones

Abstract A series of 1-acetoxy-3-aryloxypropan-2-ones 1a–m were synthesized and subjected to biotransformation by bakers yeast yielding optically active monoacetates 5 or ent - 5 and/or diols 4 of moderate to excellent enantiomeric purity. The dependence of the reduction/hydrolysis ratio and stereoselectivity on the size and substitution pattern of the aromatic moiety in the substrate is also discussed.

Kinetic resolution of 1-(benzofuran-2-yl)ethanols by lipase-catalyzed enantiomer selective reactions

Abstract Kinetic resolution of racemic 1-(benzofuran-2-yl)ethanols rac - 1a – d was performed by lipase-catalyzed enantiomer selective acylation ( E ≫100) yielding (1 R )-1-acetoxy-1-(benzofuran-2-yl)ethanes ( R )- 2a – d and (1 S )-1-(benzofuran-2-yl)ethanols ( S )- 1a – d in highly enantiopure form. The degree of enantiomer selectivity for enzymatic alcoholysis/hydrolysis processes starting from racemic 1-acetoxy-1-(benzofuran-2-yl)ethane rac - 2 was also tested under various conditions including supercritical CO 2 medium. Racemization-free lipase-catalyzed ethanolysis of the (1 R )-1-acetoxy-1-(benzofuran-2-yl)ethanes ( R )- 2a – d yielded almost quantitatively the enantiopure (1 R )-1-(benzofuran-2-yl)ethanols ( R )- 1a – d .

Lipase-catalyzed enantiomer selective hydrolysis of 1,2-diol diacetates

Abstract Enantiomer selective hydrolysis of racemic 1,2-diol diacetates (rac-2a-h) was investigated by using the inexpensive commercial porcine pancreatic lipase. The hydrolysis proceeds with variable regioselectivity but with moderate to good enantioselectivity yielding a mixture of isomeric monoacetates (3a-h and 4a-h) and unchanged diacetate enantiomers (2a-h). Evidence was found that both monoacetates (3a-h and 4a-h) are formed with the same sense of enantiomer selectivity.

Chemistry of the wittig reaction, IV Simple conversion of aldehydes to 1,1-dichloroalkane and 1,1-dichloro-1-alkene derivatives, useful intermediates for the synthesis of acetylenic compounds

Abstract The formation of 1,1-dichloroalkanes and 1,1-dichloro-l-alkenes from aldehyde is described using triphenylphosphine - carbon tetrachloride reagent system. Different products can be formed by changing the reaction conditions.

Convenient synthetic route to (+)-faranal and (+)-13-norfaranal : The trail pheromone of pharaoh's ant and its congener 1

Abstract (+)-Faranal 1a , the trail pheromone of Pharaohs ant, and its congener, (+)-13-norfaranal 1b were synthetized from chiral building block 4 employing diastereoselective carbon-carbon bond formation. The application of crude pig liver esterase enzyme for the preparation of 4 is also discussed.

Synthesis and rearrangement of 13-thiaprostanoids

Abstract Thiaprostanoids 13 were prepared by conjugate addition of mercaptane 6 to cyclopentenones 12 and 20. Novel rearrangements of these compounds to 14 and 15 were interpreted as enolate induced [1,5]-sigmatropic shift on the corresponding dehydration products 16. Preparation of the various substrates and structural elucidation of new products are described.

Baker's yeast mediated reduction of dihydroxyacetone derivatives

Several monoprotected dihydroxyacetone derivatives 4a‐d and their acetates 5a‐d were prepared and subjected to biotransformation with baker’s yeast. The simple chemical modification of the substrates (i.e. transforming the relatively small hydrophilic hydroxymethyl group into a larger hydrophobic acetoxymethyl moiety) inverted the sense of enantiotope selectivity of these reductions yielding optically active diols 6a‐d, or their enantiomeric acetates (7a‐d) and diols (ent-6a‐d), respectively.

Kinetic resolution of trans-2-acetoxycycloalkan-1-ols by lipase-catalysed enantiomerically selective acylation

Abstract Kinetic resolution of a series of racemic trans -cycloalkane-1,2-diol monoacetates rac - 2a – d was performed by enantiomerically selective transesterification with vinyl acetate catalysed by commercial and our own-prepared fungal lipases to yield diacetates ( R , R )- 3a – d and monoacetates ( S , S )- 2a – d in high enantiomeric purity. The monoacetates ( R , R )- 2a – d were also prepared from the racemic diacetates rac - 3a – d by lipase-catalysed hydrolysis.

Baker's yeast mediated synthesis of (5SR, 9S)-5,9-dimethyl-heptadecane and (5SR, 9S)-5,9-dimethyl pentadecane; the main sex-pheromone components of Leucoptera scitella and Perileucoptera coffeella enriched in 9S-isomers

Abstract A mixture of (5 S , 9 S )-5,9-dimethyl heptadecane ( 1a ), the main sex-pheromone component of Leucoptera scitella , and its (5 R , 9 S )-isomer ( 2a ) was synthetized conveniently from ( R )-citronellal ( 4 , obtained from racemic citronellal by enantiomer selective bakers yeast reduction) in four steps. (5 SR , 9 S )-5,9-Dimethyl-pentadecane (mixture of 1b and 2b ), a possible sex-attractant of Perileucoptera coffeella was prepared analogously.