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Heterogeneous catalysts based on Sm-doped ceria were employed for the first time in the liquid-phase oxidation of α-bisabolol. Nanometer-sized catalysts were obtained by microwave-hydrothermal synthesis and were characterized by X-ray diffraction (XRD), temperature programmed reduction (TPR), Raman spectroscopy and N2-physisorption. The influence of Sm doping, temperature and the solvent used on the catalytic behavior was investigated. Conversions up to 84% and a combined selectivity for the products up to 77% were obtained for Ce0.9Sm0.15O 1.85-δ catalysts. The reactions were highly selective for the epoxidation products (only bisabolol oxides A and B were obtained) and shown to be strongly dependent on the temperature and solvent employed. Best results were achieved for higher Sm concentrations, which indicate that changes in the textural properties due to doping produced a significantly more active catalyst.

Two norditerpenoids (1-2) with unique carbon skeletons, four sesquiterpenoids (3-6) and nine nor-sesquiterpenoids (7-15) were isolated from the leaves of Crataegus pinnatifida and evaluated as possessing antithrombotic activities in vitro/vivo. Their structures with absolute configurations were determined via a combination of spectroscopic data, chemical methods, and quantum-chemical calculations (ECD, NMR, and OR data). Compound 3 showed an inhibitory effect on ADP induced platelet aggregation in vitro, which is mediated through the response to the specific receptor of P2Y12 by docking results. Compound 3 also clearly prolonged the time to form thrombocytes induced by FeCl3, in the caudal vessels of zebrafish.

Plant peroxygenase (PXG) oxidizes unsaturated fatty acids by transferring an oxygen atom of a hydroperoxide to the double bond, thereby providing epoxides. In this work we investigated the potential of a PXG from tomato (Solanum lycopersicum, SlPXG) to catalyze the oxidation of a variety of natural products. A SlPXG gene was cloned from tomato, heterologously expressed in yeast and the membrane bound recombinant SlPXG protein was used as enzyme source. Unsaturated fatty acids, fatty acid derivatives, and terpenes were epoxidized by SlPXG in the presence of various hydroperoxides exclusively at their cis-double bonds. Terpenes with p-menthene skeleton were transformed in different ways depending on their molecular structures. R-(+)- and S-(-)-limonene were converted to R-(+)-limonene-trans-1,2-epoxide (97%) and cis-S-(-)-limonene-1,2- epoxide (88%), respectively whereas α-terpinenewas hydroxylated to cis-1,4-dihydroxy-p-menth-2-ene and γ-terpinene was aromatized to p-cymene. In the last reaction the hydroperoxide served as hydrogen acceptor rather than an oxygen donor. PXG appears to be a versatile biocatalyst able to perform different kinds of oxidation reactions. As no cofactors like NAD(P)H are required and H2O2is an environmentally friendly oxidant, PXG enables new applications for the synthesis of fine chemicals from renewable resources.

Vanadium(v) complexes 4 have been prepared from tridentate Schiff-base ligands 3 and VO(OEt)3. All vanadium(v) compounds were characterized (IR, UV/Vis, and 51V NMR spectroscopy, and in selected examples by X-ray diffraction analysis) and were applied as oxidation catalysts for the stereoselective synthesis of functionalized tetrahydrofurans 2 starting from substituted bis(homoallylic) alcohols 1 (mono- or trisubstituted C-C double bonds). Oxidation of secondary or tertiary 1-alkyl-, 1-vinyl-, or 1-phenyl-substituted 5,5-dimethyl-4-penten-1-ols under optimized conditions [TBHP as primary oxidant and 1,2-(amino)indanol-derived vanadium(v) reagent 4g as catalyst] provided 2,5-cis-configured tetrahydrofurans in synthetically useful yields and diastereoselectivities (22-96% de). On the other hand, trans-disubstituted oxolanes (62%-96 de) were obtained from oxidations of 2- or 3-alkyl- and 2- or 3-phenyl-substituted 5,5-dimethyl-4-penten-1-ols bis(homoallylic) allyhc) alcohols. Treatment of 4-penten-1-ols (i.e. substrates with monosubstituted olefinic π-bonds) with TBHP and catalytic amounts of vanadium(v) complex 4g furnished trans-disubstituted tetrahydrofurans as major products (20-96% de), no matter whether an alkyl or a phenyl substituent was located in position 1, 2, or 3 of the alkenol chain. The mechanism of this reaction has been investigated in detail. Based on results from 51V NMR spectroscopy and competition kinetics, it proceeds by a transition metal-peroxy pathway. In an initial step, TBHP coordinates to, for example, N-(2-oxidophenyl)salicylideniminato-derived vanadium complex 4a. Subsequent alkenol binding gives rise to a "loaded" vanadium(v) peroxy complex (e.g. 60) which facilitates diastereoselective oxygen transfer, presumably onto a coordinated substrate. This step leads to the formation of functionalized tetrahydrofurans as major products. TBHP binding to the remaining vanadium(v) complex then allows a regeneration of the active oxidant, for example peroxy complex 57. The origin of the observed diastereoselectivity in this oxidation has been studied in an independent stereochemical analysis. Thus, diastereomerically enriched epoxy alcohol (1R,4R)-10 was prepared. Its treatment with 1,2-(amino)indanol-derived vanadium complex 4g affords a 91:9 mixture of cis-2-(1-hydroxy-1-methylethyl)-5-(phenyl)tetrahydrofuran (cis-6) and cis-2,2-dimethyl-6-(phenyl)tetrahydropyran-3-ol (cis-7). Similarly, a 39:61 mixture of heterocycles trans-6 and trans-7 was obtained from epoxy alcohol (1S,4R)-10, if treated with Lewis acid 4g. ( Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003).

The stereochemistry of the bisaboloids in chamomile - with the exception of bisabololoxide C - has been elucidated.The in-vitro-examination of the mutual convertibilities of some bisaboloids gave evidence for the stereochemical accordance of the common chiral centres of all the bisaboloids.The absolute configurations of the remaining third asymmetric carbon atoms in bisabololoxide A and B have been determined by NMR spectrometric studies in comparison with their unnatural semisynthetic epimers.All the stereogenic centres of the bisabololoxides A and B, of (-)-α-bisabolol and of bisabolonoxide A turn out to be S-configurated. - Key words: Matricaria chamomilla L., Bisaboloids, 13C NMR Spectra, Shift-Reagents