Configuration Of Stereogenic Center Research Articles

New chiral Mannich adducts of di-tert-butylphenols and a bicyclic imine – Synthesis and antiproliferative activity

Tests of antiproliferative activity of Mannich adducts of aromatic nucleophiles and a chiral bicyclic imine revealed a di-tert-butylphenol derivative as a promising compound for further exploration. To study the influence of substitution pattern and a configuration of stereogenic centers on the inhibition of cancer cell growth, a series of Mannich bases were obtained with a good to high diastereoselectivity from the reaction of the imine and three isomeric di-tert-butylphenols. Six new enantiopure adducts were isolated and fully characterized. Selected derivatives were shown to exhibit an interesting antiproliferative activity comparable to cisplatin.

Structural Aspects and Host Effects of the Chirality Transfer by Mesogenic Substituted Aminoalcohols

ABSTRACTIn continuation of the investigations on chiral dopants derived from the aminoalcohols ephedrine and pseudoephedrine as chiral bivalent structure elements, a series of new agents bearing very different substituents has been synthesized. The products turned out to be suited for preparation of short-pitch chiral liquid crystalline (LC) phases and were characterized by measuring their helical twisting power (HTP) in nematic host mixtures. In particular cases, structural features on the molecular level of dopants in relation to host constitution will be discussed. On the other hand, macroscopic properties, such as dynamic and dielectric data of achiral host systems, have been considered to find out practically useful guidelines for tailoring chiral LC guest–host systems. The studies include recording of nuclear magnetic resonance (NMR) spectra to study the dependence of helicity induction on the configuration of stereogenic center. Further, some photostability tests of cholesteric mixtures reflecting light in the visible range have been undertaken with regard to exploiting these dopants in electro-optic liquid crystal devices such as cholesteric bistable displays.

A New Cyclopropyl‐Triterpenoid from Ochradenus arabicus

AbstractOne new cyclopropyl‐triterpenoid (1), along with four known constituents including octacosan‐1‐ol (2), pentacosanoic acid (3), β‐sitosterol (4), and β‐sitosterol 3‐O‐β‐D‐glucopyranoside (5) were isolated from the aerial parts of Ochradenus arabicus for the first time. These compounds were isolated by repeated column chromatography followed by further purification through recycling HPLC. The structure of the new secondary metabolite 1 was established on the basis of UV, IR, 1D‐ (1H‐ and 13C‐) and 2D‐NMR (HMBC and HSQC), and MS spectral data. The molecular mass was determined by HR‐MS, and hence the molecular formula was deduced. The configurations of stereogenic centers in the molecule were assigned by NOESY experiments, along with biogenetic considerations. The structures of the known compounds were confirmed by comparison of their physical and spectroscopic data with those reported in literature.

Reactions of hydrogen peroxide with acetylacetone and 2-acetylcyclopentanone

A reaction of acetylacetone with equimolar amount of concentrated aqueous H2O2 in both organic solvents (ButOH, AcOH) and water at various temperatures gave the corresponding 3,5-dihydroxy-1,2-dioxolanes with different configuration of stereogenic centers. In the presence of an excess of H2O2, 3,5-dihydroxy-1,2-dioxolanes were converted to a mixture of 5-hydroperoxy-3-hydroxy-1,2-dioxolanes and further to a mixture of dimeric 1,2-dioxolan-3-ylperoxides. All the peroxides formed exist in solutions as equilibrium mixtures with the starting reagents. A prolonged reflux of solutions of 3,5-dihydroxy-1,2-dioxolanes in ButOH in the presence of a large excess of H2O2 led to the skeletal rearrangements of the substrates to a mixture of propionic acid and hydroxyacetone, which underwent further oxidative transformations. Unlike acetylacetone, 2-acetylcyclopentanone reacted with H2O2 in aqueous phase or in solutions in ButOH under thermodynamic or kinetic control with the formation of the corresponding 5-hydroperoxy-3-hydroxy-1,2-dioxolanes, rather than 3,5-dihydroxy-1,2-dioxolanes. Thermodynamically controlled process in solution in AcOH gave a mixture of all four possible hydroperoxyhydroxy-1,2-dioxolanes. These cyclic peroxides in solutions in ButOH or AcOH readily converted to a mixture of AcOH, glutaric, α-methyladipic, and α-hydroxy-α-methyladipic acids. An active α-hydroxylation of the substrate was observed upon reflux of a solution of 2-acetylcyclopentanone and H2O2 in AcOH.

ChemInform Abstract: Novel Chiral 1-(Ferrocenylalkyl)-(S)-prolinols and Their Application in Enantioselective Synthesis.

Abstract Diastereomeric ferrocenylphosphine ligands, (−)-( S , R , pS )-BPPF-Pro ( 3a ) and (+)-( S , S , pR )-BPPF-Pro ( 3b ), containing the ( S )-prolinol moiety were prepared. A detailed structural elucidation of these ligands was carried out using NMR. The Pd-complexes of these ligands were used for enantioselective catalysis of allylic substitution reactions of rac -( E )-1,3-diphenyl-3-acetoxyprop-1-ene with C-nucleophiles generated from pentan-2,4-dione and dimethyl malonate. A series of chiral ferrocene aminoalcohols with ( S )-prolinol moiety ( 4a – c ) were also prepared. The role of the configuration of stereogenic centers for stereoselectivity in diethylzinc addition to benzaldehyde was studied.