Regio- and Stereoselective Synthesis of Functionalized Dihydropyridines, Pyridines, and 2H-Pyrans: Heck Coupling of Monocyclopropanated Heterocycles.

A palladium-catalyzed coupling between aryl halides and monocyclopropanated pyrroles or furans has been developed, leading to valuable six-membered N- and O-heterocycles. As the key step, a selective cleavage of the non-activated endocyclic C-C bond of the 2-heterobicyclo-[3.1.0]hexane framework is achieved. The developed method offers access to highly functionalized piperidines, pyridines, and pyrans that are challenging to access by traditional methods.

Acyclic Remote 1,5- and 1,4,5-Stereocontrol in the Catalytic Stereoselective Reactions of ß-Lactams with Aldehydes: The Effect of the N-Methylimidazole Ligand.

The application of the N-methylimidazole ( N-MI) ligand in the Pd(0)/InI-promoted allylations of aldehydes with ß-lactam-derived organoindiums enables the reaction of azetidin-2-ones with diversely substituted allyl moieties, inert under previously reported conditions. As a result, allylations and crotylations of a variety of aromatic and aliphatic aldehydes with previously unavailable chiral ε-amido-allylindiums bearing α-, ß-, or γ-substituted allyl fragments were developed. The reactions occur under thermodynamic control with a highly efficient remote 1,5- or 1,4,5-stereocontrol to afford a diversity of (3 Z)-2,5- anti-2,6- syn- or (3 Z)-2,5- syn-2,6- anti-substituted enediols, aminoalcohols, and homoallylic alcohols in moderate to high yields and with an excellent diastereoselectivity. A detailed study on the effect of the ß-lactam and aldehyde structures and chirality on the yield and stereochemistry in the products was carried out.

Chemical composition of edible aerial parts of meadow bistort (Persicaria bistorta (L.) Samp.).

Persicaria bistorta (syn. Polygonum bistorta) is a herbaceous plant native to Europe and Asia. The leaves, young shoots or aerial parts of bistort are one of the main ingredients in a savoury pudding common to parts of the North of England. The aim of the present study was to investigate the chemical composition of extracts from aerial parts of common bistort. The UHPLC method allowed the detection of thirty-five major and minor compounds in the analysed plant material. Major constituents were isolated and identified. Two new natural products were obtained namely quercetin and kaempferol 3-O-(5″-O-malonyl)-α-l-arabinofuranosides. The bioactivity assays showed that isolated malonylated flavonoids inhibit the production of reactive oxygen species (IC50 in the range 22.4-40.6µM) and myeloperoxidase release (IC50 in the range 22.2-32.2µM) from stimulated human neutrophils. Aerial parts of P. bistorta are a rich source of polyphenols and some of them have anti-inflammatory potential.

Effective 1,5-stereocontrol in Pd(0)/InI promoted reactions of chiral N-Ts-4-vinylazetidin-2-ones with aldehydes. An efficient entry into nonracemic semi-protected (3Z)-2,6-anti-enediols.

ε-Amido-allylindiums generated in situ from N-Ts-4-vinylazetidin-2-ones in the presence of 2 eq. of InI and catalytic amounts of Pd(PPh3)4 react with a number of aromatic and aliphatic aldehydes with effective remote 1,5-stereocontrol to afford (3Z)-2,6-anti-enediols as major products in good yields and with excellent diastereoselectivity.

Double bond stereochemistry influences the susceptibility of short-chain isoprenoids and polyprenols to decomposition by thermo-oxidation.

Isoprenoid alcohols are common constituents of living cells. They are usually assigned a role in the adaptation of the cell to environmental stimuli, and this process might give rise to their oxidation by reactive oxygen species. Moreover, cellular isoprenoids may also undergo various chemical modifications resulting from the physico-chemical treatment of the tissues, e.g., heating during food processing. Susceptibility of isoprenoid alcohols to heat treatment has not been studied in detail so far. In this study, isoprenoid alcohols differing in the number of isoprene units and geometry of the double bonds, ß-citronellol, geraniol, nerol, farnesol, solanesol and Pren-9, were subjected to thermo-oxidation at 80 °C. Thermo-oxidation resulted in the decomposition of the tested short-chain isoprenoids as well as medium-chain polyprenols with simultaneous formation of oxidized derivatives, such as hydroperoxides, monoepoxides, diepoxides and aldehydes, and possible formation of oligomeric derivatives. Oxidation products were monitored by GC-FID, GC-MS, ESI-MS and spectrophotometric methods. Interestingly, nerol, a short-chain isoprenoid with a double bond in the cis (Z) configuration, was more oxidatively stable than its trans (E) isomer, geraniol. However, the opposite effect was observed for medium-chain polyprenols, since Pren-9 (di-trans-poly-cis-prenol) was more susceptible to thermo-oxidation than its all-trans isomer, solanesol. Taken together, these results experimentally confirm that both short- and long-chain polyisoprenoid alcohols are prone to thermo-oxidation.

Synthesis of ß- and γ-hydroxy α-amino acids via enzymatic kinetic resolution and cyanate-to-isocyanate rearrangement.

A new strategy for stereoselective preparation of all four isomers of ß- and γ-hydroxy α-amino acids is presented. The developed procedure is based on enzymatic kinetic resolution and cyanate-to-isocyanate rearrangement as key steps. Stereocontrol is achieved by proper choice of the starting hydroxyacid, the course of kinetic resolution, and the stereospecific sigmatropic rearrangement step, which proceeds with full chirality transfer.