Marek Krzemiński

Dual Stereoselectivity in the Dialkylzinc Reaction Using (−)-β-Pinene Derived Amino Alcohol Chiral Auxiliaries

(+)-Nopinone, prepared from naturally occurring (-)-beta-pinene, was converted to the two regioisomeric amino alcohols 3-MAP and 2-MAP in very good yield and excellent isomeric purity. Amino alcohol 3-MAP was synthesized by converting (+)-nopinone to the corresponding alpha-ketooxime. This was reduced to the primary amino alcohol and was converted to the morpholino group through a simple substitution reaction. 3-MAP was characterized by X-ray crystallography, which displayed the rigidity of the pinane framework. Amino alcohol 2-MAP was prepared from its trans isomer 2, which in turn was synthesized via hydroboration/oxidation of the morpholine enamine of (+)-nopinone. Two-dimensional NMR was used to characterize amino alcohol 2-MAP, and NOE was used to confirm its relative stereochemistry. These amino alcohols were employed as chiral auxiliaries in the addition of diethylzinc to benzaldehyde to obtain near-quantitative asymmetric induction in the products. The use of 3-MAP yielded (S)-phenylpropanol in 99% ee, and its regioisomer 2-MAP gave the opposite enantiomer, (R)-phenylpropanol, also in 99% ee. Other aromatic, aliphatic, and alpha,beta-unsaturated aldehydes were implemented in this method, affording secondary alcohols in high yield and enantiomeric excess. Amino alcohols 2-MAP and 3-MAP were also found to be useful in the dimethylzinc addition reaction, both catalyzing the addition to benzaldehyde with nearly quantitative ee. Regioisomeric amino alcohols 2-MAP and 3-MAP, even though they were prepared from one enantiomer of nopinone, provide antipodal enantiofacial selectivity in the dialkylzinc addition reaction. This circumvents the necessity to synthesize amino alcohols derived from (-)-nopinone, which in turn requires the unnatural (+)-beta-pinene. Possible mechanistic insights are offered to explain the dual stereoselectivity observed in the diethylzinc addition reaction involving regioisomeric, pseudo-enantiomeric amino alcohols 3-MAP and 2-MAP.

Asymmetric reduction of ketoxime derivatives and N-alkylketimines with borane–oxazaborolidine adducts

Abstract Oxime ethers of acetophenone, isopropyl methyl ketone, and tert-butyl methyl ketone were reduced to the corresponding hydroxylamine ethers of 45–94% ee with borane–oxazaborolidine 1 derived from (−)-norephedrine. A one-pot reduction of acetophenone oxime with 1 to 1-phenylethylhydroxylamine of 87% ee is described. The reduction of 6-methyl-2,3,4,5-tetrahydropyridine and N-methylimines of the above mentioned ketones with borane-B-methyloxazaborolidine adduct 2, derived from (−)-diphenylprolinol, gave the corresponding amines of 40–74% ee.

New procedure of selected biogenic amines determination in wine samples by HPLC

A new procedure for determination of biogenic amines (BA): histamine, phenethylamine, tyramine and tryptamine, based on the derivatization reaction with 2-chloro-1,3-dinitro-5-(trifluoromethyl)-benzene (CNBF), is proposed. The amines derivatives with CNBF were isolated and characterized by X-ray crystallography and (1)H, (13)C, (19)F NMR spectroscopy in solution. The novelty of the procedure is based on the pure and well-characterized products of the amines derivatization reaction. The method was applied for the simultaneous analysis of the above mentioned biogenic amines in wine samples by the reversed phase-high performance liquid chromatography. The procedure revealed correlation coefficients (R(2)) between 0.9997 and 0.9999, and linear range: 0.10-9.00 mg L(-1) (histamine); 0.10-9.36 mg L(-1) (tyramine); 0.09-8.64 mg L(-1) (tryptamine) and 0.10-8.64 mg L(-1) (phenethylamine), whereas accuracy was 97%-102% (recovery test). Detection limit of biogenic amines in wine samples was 0.02-0.03 mg L(-1), whereas quantification limit ranged 0.05-0.10 mg L(-1). The variation coefficients for the analyzed amines ranged between 0.49% and 3.92%. Obtained BA derivatives enhanced separation the analytes on chromatograms due to the inhibition of hydrolysis reaction and the reduction of by-products formation.

Syntheses with organoboranes. VI. Kinetic resolution of vinylic epoxides by the reduction with chiral dialkylboranes

Abstract The synthesis of enantiomerically enriched 2-vinyloxirane and monoepoxides of 1,3-cycloalkadienes by kinetic resolution of racemates with Ipc 2 BH, 2- d Icr 2 BH and 4- d Icr 2 BH of high enantiomeric purity is described.

Synthesis of novel octyl sinapate to enhance antioxidant capacity of rapeseed–linseed oil mixture

BACKGROUND Lipophilisation allows the formation of new functionalised antioxidants having beneficial properties compared to natural hydrophilic phenolic acids. Therefore, this work focused on the synthesis of lipophilic antioxidants, such as a new octyl sinapate, octyl caffeate and octyl ferulate using the modified Fischer esterification of selected hydroxycinnamic acids with 1-octanol. RESULTS The lipophilic octyl sinapate was obtained for the first time with satisfactory yield (83%) after purification by column chromatography. The identity of the synthesised phenolipids was confirmed by chromatographic and spectroscopic analyses. Antioxidant capacity of phenolipids was determined by DPPH (IC50  = 35.87-52.24 μg mL-1 ) and ABTS (IC50  = 39.45-48.72 μg mL-1 ) methods and compared with IC50 values (7.37-35.30 μg mL-1 and 7.55-41.67 μg mL-1 , respectively) for well known antioxidants. The antioxidant capacity of rapeseed-linseed oil enriched with the purified esters was about two to 30 times higher in comparison with a non-supplemented oil. CONCLUSION The novel octyl sinapate as well as octyl caffeate and octyl ferulate have antioxidant properties and lipophilic character, therefore they may be added to vegetable oils as potential antioxidants for tackling oxidative processes.

Application of 3,5-bis-(trifluoromethyl)phenyl isothiocyanate for the determination of selected biogenic amines by LC-tandem mass spectrometry and 19F NMR

3,5-Bis-(trifluoromethyl)phenyl isothiocyanate, was used as a convenient reagent for the derivatization of histamine, tyramine, tryptamine and 2-phenylethylamine, which eliminates the purification step. The obtained derivatives were determined by liquid chromatography-tandem mass spectrometry (LC-MS/MS). Additionally, the total amount of these amines was determined by 19F nuclear magnetic resonance analysis. The procedures were optimized and validated for linearity, limit of detection and quantification, intra- and inter-day precision and recovery resulting in good reproducibility and accuracy. The reagent was applied for determination of the above mentioned biogenic amines in beverages, and permitted an undemanding separation and determination of the derivatives. Moreover, it is a convenient reagent for analysis of the total amine content by quantitative 19F NMR.

New PHOX ligands monoterpene derivatives and their application in catalytic transfer hydrogenation of ketones

In this paper we present synthesis new PHOX ligands α- and β-pinene derivatives. We applied their ruthenium (I) complexes in asymmetric catalytic transfer hydrogenation of ketones with good yields and enantioselectivity.