Measurement of CP-violating asymmetries in B0 decays to CP eigenstates.

We present measurements of time-dependent CP-violating asymmetries in neutral B decays to several CP eigenstates. The measurement uses a data sample of 23x10(6) Upsilon(4S)-->BbarB decays collected by the BABAR detector at the PEP-II asymmetric B Factory at SLAC. In this sample, we find events in which one neutral B meson is fully reconstructed in a CP eigenstate containing charmonium and the flavor of the other neutral B meson is determined from its decay products. The amplitude of the CP-violating asymmetry, which in the standard model is proportional to sin2beta, is derived from the decay time distributions in such events. The result is sin2beta = 0.34+/-0.20 (stat)+/-0.05 (syst).

Cyclization of geranylgeranyl diphosphate to taxa-4(5),11(12)-diene is the committed step of taxol biosynthesis in Pacific yew.

The biosynthesis of taxol (paclitaxel) and related taxoids in Pacific yew (Taxus brevifolia) is thought to involve the cyclization of geranylgeranyl diphosphate to a taxadiene followed by extensive oxygenation of this diterpene olefin intermediate. A cell-free preparation from sapling yew stems catalyzed the conversion of [1-3H]geranylgeranyl diphosphate to a cyclic diterpene olefin that, when incubated with stem sections, was converted in good radiochemical yield to several highly functionalized taxanes, including 10-deacetyl baccatin III and taxol itself. Addition of the labeled olefin to a yew bark extract, followed by radiochemically guided fractionation, provided sufficient product to establish the structure as taxa-4(5),11(12)-diene by two-dimensional NMR spectroscopic methods. Therefore, the first dedicated step in taxol biosynthesis is the conversion of the universal diterpenoid precursor geranylgeranyl diphosphate to taxa-4(5),11(12)-diene, rather than to the 4(20),11(12)-diene isomer previously suggested on the basis of the abundance of taxoids with double bonds in these positions. The very common occurrence of taxane derivatives bearing the 4(20)-ene-5-oxy functional grouping, and the lack of oxygenated derivatives bearing a 4(5)-double bond, suggest that hydroxylation at C-5 of taxadiene with allylic rearrangement of the double bond is an early step in the conversion of this olefin intermediate to taxol.

Diterpenoid resin acid biosynthesis in conifers: enzymatic cyclization of geranylgeranyl pyrophosphate to abietadiene, the precursor of abietic acid.

Abietic acid is a major component of the rosin fraction of oleoresin synthesized by conifer species, such as grand fir (Abies grandis) and lodgepole pine (Pinus contorta), as a defensive secretion against insect and pathogen attack. This diterpenoid resin acid is derived from geranylgeranyl pyrophosphate by conversion to abietadiene and sequential oxidation of the C18-methyl group of the precursor olefin to a carboxyl function. Resin acid biosynthesis is constitutively expressed at high levels in lodgepole pine stem and is induced to these levels by stem wounding in grand fir. Soluble enzyme extracts of lodgepole pine stem and of mechanically wounded grand fir stem catalyzed the divalent metal ion-dependent cyclization of [1-3H]geranylgeranyl pyrophosphate to (-)-abieta-7(8),13(14)-diene. The wound-inducible enzyme was partially purified and identified as an 80-kDa protein with general characteristics typical of those of other terpenoid cyclases. Although the enzymatic cyclization sequence almost certainly involves the formation of copalyl pyrophosphate and a pimaradiene as stable intermediates, no evidence for the separation of the corresponding partial activities was obtained. A pathway involving the production of various pimaradiene and abietadiene isomers is proposed to account for the origin of several common resin acids.

Hydride shifts in the biosynthesis of the p-menthane monoterpenes alpha-terpinene, gamma-terpinene, and beta-phellandrene.

The biosynthesis of several monoterpenes from the acyclic precursor geranyl pyrophosphate requires the migration of positive charge from the isopropyl side chain into the cyclohexenoid ring of the universal alpha-terpinyl cation intermediate of the reaction. The hydride shifts responsible for charge migration in the formation of three p-menthane olefin isomers were examined in a range of plant species: alpha-terpinene in American wormseed, gamma-terpinene in thyme, and (-)-beta-phellandrene in lodgepole pine. The experimental approach utilized soluble cell-free enzyme systems and specifically labeled geranyl substrates, with the determination of the labeling patterns in the resulting cyclic products. The results were consistent with stereoelectronic features of the cyclization and support the general model for monoterpene formation.