Tocopherols, collectively known as vitamin E, are only synthesised in photosynthetic organisms. Tocopherol cyclase (TC) catalyses the formation of the chromanol headgroup of the various tocopherol isoforms. TCs from Arabidopsis and maize (Zea mays) were expressed in Escherichia coli and purified. Analysis of the enzymatic properties revealed similarities but also differences between the two enzymes. Overexpression of chimeric TC gene constructs in developing seeds of transgenic rapeseed plants enhanced and modified the relative abundance of individual tocochromanol species in the seed oil, indicating a regulatory function of the enzyme in prenyllipid metabolism.
The first highly efficient asymmetric synthesis of the diketotriterpenoid 1, isolated from the Indonesian marine sponge Hyrtios erectus, in good overall yield and employing simple starting materials such as butanone, is described. Both stereogenic centres at the C-6 and C-19 positions of the C 2 -symmetrical molecule were generated via a-alkylation employing the SAMP/RAMP hydrazone method with high asymmetric inductions (de, ee ³ 96%). The absolute configuration of the natural material was determined as R,R.
Mal nicht elektrophil: Eine neue, nucleophile Reaktionsweise von Organopalladiumspezies wurde aufgedeckt. Die Reaktion von Arylisocyanaten mit terminalen Alkinen in Gegenwart eines Palladiumkatalysators führt über eine intramolekulare Vinylpalladierung von Isocyanaten zu Oxindolprodukten (siehe Schema; dppe=1,2‐Bis(diphenylphosphanyl)ethan).
The asymmetric synthesis of the female-produced sex pheromone of the caddisÑy Hesperophylax occidentalis, (S)and (R)-6-methyl-3-nonanone, starting from the simple starting materials propanal, propyl iodide and 2-butanone, in good overall yields is described. The stereogenic centre at the C-6 position of the pheromone was generated via a-alkylation employing the SAMP/RAMP hydrazone method with high asymmetric induction (ee \ 94 and 92%).
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